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Full text of "Guidebook to Constructing Inexpensive Science Teaching Equipment, Physics"

GUIDEBOOK TO CONSTRUCTING 



INEXPENSIVE SCIENCE TEACHING EQUIPMENT 



Volume III: Physics 



Inexpensive Science Teaching Equipment Project 



Science Teaching Center 



University of Maryland, College Park 



U.S.A. 



©Copyright. The contents of this Guidebook are open to thti publicdomain except 
for those items which have been taken directly (as opposed to adapted from other 
sources, and which are identified within the text by the symbol © Permissjon to 
reproduce copyright items should be obtained directly fromthe relevant authors 

June 1972 



Inexpensive Science Teaching Equipment Project 

Science Teaching Center 

University of Maryland 



Project Director and Administrator 
J. David Lockard 

Survey Team 

Mary Harbeck 
Maria Penny 



Guidebook Director 
Reginald F. Melton 



1968-72 

1968-70 
1968-70 



1970-72 



1970-72 



Writing, Drawing and Equipment Development Team 
Reginald Melton 
John Delaini 1970-72 

Donald Urbancic 1970-71 

Ruth Ann Butler 1971-72 

Technical Assistants 

David Clark 1970-72 

Chada Samba Siva Rao 1970-71 



CONTENTS 

The Guidebook is presented in three volumes: 
Volume I, Biology 
Volume I I£hemistry 
Volume II,IPhysics 

The following table refers only to the contents of this 
volume, but the listing at the back of each volume provides an 
alphabetical index to all three volumes. 

References within the text normally indicate the volume, 
chapter and, number of the item referred to (e.g., CHEM/V/A3), 
but where a reference is to an item within the same volume, the 
reference indicates only the chapter and number of the item 
( e . g .V/A3) . 

Within this volume the contents of each chapter are 
generally presented in a logical order in which items advance 
from simple to complex, from a point of view of both construction 
and educational usage. 



-11- 



Table of Contents 



Page 
Foreword v 



Raw Materials and Tools 



vm 



I. BALANCES 1 



A. ELEMENTARY BALANCES 

Al. Spring Lever Balance 2 

A2 . Rubber Band Balance 5 

A3. Simple Beam Balance 8 

B. EXPERIMENTAL BALANCES 

Bl. Extending Spring Balance 9 

B2 . Compression Spring Balance 12 

B3. Pegboard Balance 17 

B4. Soda Straw Balance 20 

B5. Microbalance 22 

C. FUNCTIONAL BALANCES 

CI. Equal Arm Balance 24 

c2. Box of Masses 30 

c3. Single Pan Balance 32 

c4. Spring Balance 36 

I I . TIMING DEVICES 40 



A. LONG INTERVAL TIMERS 

Al. Sun Dial 41 

A2 . Water Clock 44 

B. MEDIUM INTERVAL TIMERS 

Bl. Pulse 49 

B2. Simple Pendulum 50 

B3. Classroom Clock 52 

C. SHORT INTERVAL TIMERS 

CI. Ticker Tape Timer 56 

III. CARTS 60 



A. FORCE AND MOTION CARTS 

Al. Elementary Cart 61 

A2 . Lightweight Cart 66 

A3. Heavyweight Cart 75 

IV. WAVE MOTION APPARATUS 80 



A. RIPPLE TANK APPARATUS 

Al. Ripple Tank 81 

A2 . Ripple Tank Accessories 90 

A3, Stroboscope 93 



-m- 



V. THE MULTIPURPOSE SYRINGE 95 

A. AIR PRESSURE APPARATUS 

Al. Hydraulic Press 96 

A2 . Vacuum Apparatus 99 

A3. Elasticity Device 102 

A4. Gas Expansion Device 103 

B. SPECIFIOGRAVITY APPARATUS 

Bl. Volume Determinator 105 

B2 . Specific Gravity Device 107 

B3. Hydrometer 108 

VI, OPTICS APPARATUS 110 

A. GENERAL APPARATUS 

Al. Light Source 111 

A2 . Slit/Aperture Combination 113 

B. REFLECTION APPARATUS 

Bl. Mirrors and Electroplating 116 

B2 . Optical Board and Accessories 119 

C. REFRACTION APPARATUS 

CI. Optical Prisms and Lenses 121 

C2. Screen with Holder 124 

c3. Refraction Model Apparatus 126 

c4. Filter 128 

D. LENS APPARATUS 

Dl. Lens with Holder 130 

D2. Multiple Slits 133 

E. DIFFRACTION AND INTERFERENCE APPARATUS 

El. Fixed Single and Double Slits 134 

E2. Adjustable Single Slit 136 

E3. Diffraction Holes 137 

E4. Interference Strips 138 

VII. LABORATORY ACCESSORIES 139 

A. TRANSFORMERS 

Al . Transformer, Iron Wire Core 140 

(6 volt output, 120 volt mains) 

A2 . Transformer, Sheet Iron Core 147 
(12 volt output, 120 volt mains) 

A3. Transformer, Variable Output 153 
(120 volt mains) 

B. RECTIFIERS 

Bl. Sodium Carbonate Rectifier (2 Plate) 162 

B2. Silicon Rectifier 168 



VIII. CIRCUIT APPARATUS 17 6 

A. CELLS 

Al. Chemical Cell 177 

A2. Dry Cell Holder with Cells 180 

A3. Simple Battery la5 

B. CIRCUIT COMPONENTS 

Bl. Bulb Holder with Bulb 191 

B2. Switch 193 

B3. Circuit Board 195 

C. RESISTORS 

CI. Variable Resistor (Carbon) 202 

c2. Variable Resistor (Nichrome) 204 

c3. Decade Resistor 209 

D. DYNAMO/MOTORS 

Dl. Simple Motor 212 

D2. Dynamo/Motor 217 

IX. ELECTROMAGNETISMAPPARATUS 230 



A. ELECTROMAGNETISM APPARATUS 

Al. Magnetizing Coil and Magnets 231 

A2. Multipurpose Coil with Cores 235 

A3. Magnetic Field Apparatus 238 

A4 . Magnetic Field Apparatus with Multipurpose Coils 241 

X. GALVANOMETERS 2 45 

A . ELEMENTARY GALVANOMETERS 

Al. Elementary Tangent Galvanometer 246 

A2 . Repulsion Type Galvanometer 249 

A3. Hot Wire Ammeter 255 

A4. Current Balance 261 

A5. Elementary Moving Coil Galvanometer 266 

B. FUNCTIONAL TANGENT GALVANOMETERS 

Bl. Tangent Galvanometer 272 

B2 . Tangent Galvanometer with Shunts 276 

C. MOVING COIL GALVANOMETER 

CI. Moving Coil Galvanometer 285 

c2. Moving Coil Galvanometer with Multipurpose Coils 292 

c3. Moving Coil Galvanometer with Shunts 296 

Bibliography 3Qg 

Alphabetical Index 3Q9 



FOREWORD 



History 

The Inexpensive Science Teaching Equipment Project was initiated by Dr. J. David 
Lockard, and got underway under his direction in the summer of 1968. Originally entitled 
the Study of Inexpensive Science Teaching Equipment Worldwide (IS-TEW or IS-2 Study) , 
the Project was to (1) identify laboratory equipment considered essential for student 
investigations in introductory biology, chemistry and physics courses in developing 
countries; (2) improvise, wherever possible, equivalent inexpensive science teaching 
equipment; and (3) produce designs of this equipment in a Guidebook for use in develop- 
ing countries. Financial support was provided by the U.S. Agency for International 
Development through the National Science Foundation. 

The initial work of the Project was undertaken by Maria Penny and Mary Harbeck 
under the guidance of Dr. Lockard. Their major concern was the identification of 
equipment considered basic to the teaching of the sciences at an introductory level. 
An international survey was conducted, and a list of equipment to be made was compiled. 
A start was also made on the writing of guidelines (theoretical designs) for the 
construction of equipment. 

Work on the development of the Guidebook itself got underway in 1970, with the 
arrival of Reginald F. Melton to coordinate the work. Over 200 guidelines were completed 
during the year by Donald Urbancic (Biology) , Chada Samba Siva Rao and John Delaini 
(Chemistry), and Reginald Melton (Physics) . Full use was made of project materials from 
around the world which were available in the files of the International Clearinghouse ' on 
Science and Mathematics Curricular Developments, which is located in the Science 
Teaching Center of the University of Maryland. The guidelines were compiled into a 
draft edition of the Guidebook which was circulated in September, 1971, to some 80 
science educators around the world for their comments and advice. 

The work of constructing and developing equipment from the guidelines, with the 
subsequent production of detailed designs, began in a limited way in 1970, the major 
input at that time being in the field of chemistry by Chada Samba Siva Rao, who was 
with the project for an intensive two-month period. However, the main work of de Veloping 
detailed designs from the guidelines was undertaken between 1971 and 1972 by John Delaini 
(Biology) , Ruth Ann Butler (Chemistry) and Reginald Melton (Physics) . Technical 
assistance was given by student helpers, with a special contribution from David C lark, 
who was with the project for a period of 18 months. 



Thanks are due to those graduates, particularly Samuel Genova, Melvin Soboleski 
and Irven Spear, who undertook the development of specific items of equipment while 
studying at the Center on an Academic Year Institute program; to student helpers, 
especially Don Kallgren, Frank Cathell and Theodore Mannekin, who constructed the 
equipment; and to Dolores Aluise and Gail Kuehnle who typed the manuscripts. 

Last, but not least, special acknowledgement is due to those individuals, and 
organizations, around the world who responded so willingly to the questionnaires in 
1968 and to the draft edition of the Guidebook in 1971. 

The Guidebook 

The designs presented in the Guidebook are based on the premise that many students 
and teachers in developing countries will wish to make equipment for themselves. This 
does not mean that students and teachers are expected to produce all their own apparatus 
requirements. It is recognized that teachers have specific curricula to follow, and that 
"class hours" available for such work are very limited. It is also recognized that 
teachers, particularly those in developing countries, are not well paid, and often 
augment their salaries with supporting jobs, thus placing severe limits on the "out-of- 
class hours' that are available for apparatus production. 

However, in designing equipment for production by students and teachers, two factors 
have been kept in mind. One, project work in apparatus development can be extremely 
rewarding for students, bringing both students and teachers into close contact with the 
realities of science, and relating science and technology in the simplest of ways .Two, 
it is not difficult for cottage (or small scale) industries to adapt these designs to 
their own requirements. The Guidebook should therefore not only be of value to students 
and teachers, but also to cottage industries which may well be the major producers of 
equipment for schools. 

Although all the designs in the Guidebook have been tested under laboratory 
conditions in the University of Maryland, they have not been tested in school situ- 
ations nor produced and tested under local conditions in developing countries. It is 
therefore recommended that the designs should be treated primarily as limited resource 
materials to be subjected to trial and feedback. It is suggested that the first time 
that an item is constructed it should be made precisely as described in the Guidebook, 
since variations in the materials, or the dimensions of the materials, could alter the 
characteristics of the apparatus. However, once this item has been tested the producer 
is encouraged to make any number of modifications in the design, evaluating the new 
products against the original. 



Before producing new equipment in quantity, it is recommended that educators 
with experience in the field of science education should be involved in determining 
how best to make use of the Guidebook. They will wish to relate the apparatus to their 
own curriculum requirements, and, where necessary, prepare relevant descriptions of 
experiments which they recommend should be undertaken using the selected apparatus. 
They will want to subject the experiments and related equipment to trials in school 
situations. Only then will they consider large-scale production of apparatus from the 
designs in the Guidebook. At this stage educators will wish to control the quality of 
apparatus production, to train teachers to make the best use of the new apparatus, and 
to insure that adequate laboratory conditions are developed to permit full utilization 
of the apparatus. Too often in the past apparatus has sat unused on many a classroom 
shelf, simply because the teacher has been untrained in its usage, or the laboratory 
facilities have been inadequate, or because the apparatus available did not appear to 
fit the requirements of the existing curriculum. Such factors are best controlled by 
educators in the field of science education in each country . Clearly the science 
educator has a crucial role to play. 

Apparatus development, like any aspect of curriculum development, should be 
considered as a never ending process. This Guidebook is not presented as a finished 
product, but as a part of this continuing process. There is no doubt that the designs 
in this book could usefully be extended, descriptions of experiments utilizing the 
apparatus could be added, and the designs themselves could be improved. No extravagant 
claims are made concerning the Guidebook. It is simply hoped that it will contribute 
to the continuing process of development. 



TOOLS AND RAW MATERIALS 

The raw materials required to make specific items of equipment are indicated at 
the beginning of each item description. However, there are certain tools and materials 
which are useful in any equipment construction workshop, and these are listed below. 

Tools 

Chisels, Wood 

3, 6, 12, 24 mm 

(i.e., 1/8", 1/4", 1/2", 1") 

Cutters 

Bench Shears: 3 mm (1/8") 

Glass Cutter 

knife 

Razor Blades 

Scissors: 200 mm (8") 

Snips (Tinmans), Straight: 200 mm (8") 

Snips (Tinmans), Curved: 200 mm (*") 

Taps and Dies: 3 to 12 mm (1/8" to 1/2") set 



Drills and Borers 

Cork Borer Set 
Countersink, 90° 

Metal Drill Holder (Electrically Driven) , Capacity 6 mm (1/4") 
Metal Drills: 0.5, 1, 2, 3, 4, 5, 6, 7 mm 

(i.e., 1/32", 1/16", 3/32", 1/8", 5/32", 3/16", 7/32", 1/4") set 
Wood Brace with Ratchet: 250 mm (10") 
Wood Augur, Bits: 6, 12, 18, 24 mm 

(i.e., 1/4", 1/2", 3/4", 1') 

Files, Double Cut 

Flat: 100 mm, 200 mm (4" 8") 
Round: 100 mm, 200 mm (4', *") 
Triangular: 100 mm (4") 

Hammers 

Ball Pern: 125, 250, (1/4, 1/2 lb) 
Claw 250 g (1/2 lb) 

Measuring Aids 

Caliper, Inside 

Caliper, Outside 

Caliper, Vernier (may replace above two items) 

Dividers: 150 mm (6"), Toolmakers 

Meter, Electrical (Multipurpose -volts, ohms, amps, etc.) 

Meter Stick 

Protractor 

Scriber 



Measuring Aids (Continued) 

Set Square 

Square, Carpenter's: 300 mm (12") blade 

Spoke Shave: 18 mm (3/4") 

Wood Smoothing Plane 

Pliers 

Combination: 150 mm(6") 
Needle Nose: 150 mm (6") 
Side Cutting: 150 mm (6") 
Vise Grips 

Saws, Metal 

300 mm (.2") blades 

Saws, Wood 

Back Saw: 200, 300 mm (8", 12") 
Coping Saw: 200 mm (8") 
Cross Cut: 600 mm (24") 
Hand Rip: 600 mm (24") 
Key Hole Saw: 200 mm (8") 

Screw Drivers 

100 mm (4") with 2 and 3 mm tips 
150 mm (6"), with 5 mm tip 
2 00 mm (8") , with 7 mm tip 

Vises 

Metal Bench Vise: 75 mm (3") 
Wood Bench Vise: 150 mm (6") 

Miscellaneous 

Asbestos Pads 

Goggles, Glass 

Oil Can: 1/2 liter (1 pint) 

Oil Stone, Double Faced 

Punch, Center 

Sandpaper and Carborundum Paper, Assorted grades 

Soldering Iron: 60 watts, 100 watts 



Raw Materials 



Adhesives 

All Purpose Cement (Elmers, Duco) 

Epoxy Resin S Hardener (Araldite) 

Rubber Cement (Rugy) 

Wood Glue (Weldwood) 

Cellophane Tape 

Plastic Tape 

Masking Tape 



Electrical Materials 

Bulbs with Holders: 1.2, 2.5, 6.2 volts 
Dry Cells: 1.5, 6 volts 

Electrical Wire: Cotton or Plastic covered 
Fuse Wire: Assorted 
Lamps: 50, 75, 100 watts 
*Magnet Wire: #20, 22, 24, 26, 28, 30, 32, 34 
Nichrome Wire : Assorted 
Parallel Electrical Cording 
Plugs 
Switches 

Glass and Plastic 

Acrylic (Plastic) Sheets: 2 cm and 2.5 cm thick 

Plates, Glass 

Tubes, Glass: 3, 6 mm (1/8", 1/4") internal diameter 

Hardware 

8olts and Nuts, Brass or Steel; 3 mm (1/8") diameter: 12, 24, 48 mm 

(1/2", 1", 2") lengths 
NailiS, 24mm (1/2", 1") lengths 
Screws, Eye 

Screws, Wood: 12, 18, 24, 26 mm (1/2", 3/4, 1", 1 1/2") 
Thumbtacks 

Washers (Brass and Steel) : 6, 9 mm (1/4", 5/16") diameter 
Wingnuts (Steel) : 5 mm (3/16") 

Lumber 

Boxwood (Packing Case Material) 

Hardboard: 6 mm (1/4") thick 

Kiln Dried Wood: 2.5 x 15 cm (1" x 6") cross section 

1.2 x 15 cm (1/2" x 6") cross section 
Plywood: 6, 12 mm (1/4", 1/2") thickness 
Wood Dowels: 6, 12 mm (1/4", 1/2") thickness 



* U. S. Standard Plate numbers are used in this book to indicate the gauge of 
different wires. Where wires are referenced against other numbering systems 
appropriate corrections should be made in determining the gauges of materials reguired. 
The following comparison of gauges may be of interest: 

Standard Diameter of #20 Wire 

Brown S Sharp 

Birmingham or Stubs 

Washburn & Moen 

Imperial or British Standard 

Stubs' Steel 

U. S. Standard Plate 






08118 





089 





0884 





0914 





409 





09525 



Metal Sheets 

Aluminum: 0.2, 0.4 mm (1/100", 1/64") thickness. 
Brass: 0.4, 0.8 mm (1/64", 1/32") thickness . 
Galvanized Iron: 0.4 mm (1/64") thickness . 
Lead: 0.1 mm (1/250") thickness. 
Spring Steel, Packing Case Bands 

Metal Tubes: 

Aluminum, Brass, Copper: 6, 12 mm (1/4", 1/2") internal diameter. 

Metal Wires 

Aluminum: 3 mm (1/8") diameter 

Coathanger: 2 mm (1/16") diameter 
*Copper: #20, 24 

Galvanized Iron: 2 mm (1/16") diameter 
*Steel: #20, 26, 30. 

Paint Materials 

Paint Brushes 
Paint Thinner 
Varnish 
Wood Filler 

Miscellaneous 

Aluminum Foil 
Cardboard Sheeting 
Containers (Plastic or Glass) 
Corks (Rubber or Cork) 

Hinges: Assorted 

Machine Oil 

Marbles 

Mesh (Cotton, Nylon, Wire) 

Modelling Clay (Plasticene) 

Paper Clips 

Pens: Felt (Marking Pens) 

Pins and Needles 

Rubber Bands 

Soldering Lead 

Soldering Paste 

Spools 

Steel Wool 

Straws 

String (Cord, .Cotton, Nylon) 

Styrofoam 

Syringes: Assorted 

Wax (Paraffin) 



*See footnote on previous page. 



I. BALANCES 



The balances presented have been divided into three categories: 



A . ELEMENTARY BALANCE S 



These are relatively crude, but extremely easy to make, even for elementary students, 
and serve as an excellent introduction to an understanding of balances. 

B. EXPERIMENTAL BALANCES 



These are somewhat more exact and are useful for undertaking investigations into 
the properties of balance. 

C. FUNCTIONAL BALANCES 



These are relatively sophisticated and designed primarily for functional usage. 



A. ELEMENTARY BALANCES 



Al . Spring Lever Balance 



(1) Base 




a. Materials Required 
Components 

(1) Base 

(2)Scale 

(3) Spring Lever 

(4) Scale Pan 

(5)Masses 

b. Construction 

1) Base 



(3) Spring 
Lever 



(4) Scale 
Pan 



5) Masses 



Qu It ems Required 
Wood (A) 
Wood (B) 



Dimensions 

13 cm x 6 cm x 1.5 cm 

5 cm x 2.5 cm x 2.5 cm 



Wooden Strip (C) 
White Paper (D) 

Packing Case Steel Band (E) 30 cm x 1.2 cm x 0.02 cm 



2 cm x 2 cm x 0.5 cm 
15 cm x 2 cm 



Galvanized Iron Wire (F) 
Aluminum Sheet (G) 

Washers (H) 



50 cm length, #24 

5.5 cm x 5.5 cm x 
0.02 cm approximately 



Attach wood (B) to one corner 
of wood (A) to support the 
spring lever above the base. 



(2) Scale 



(3) Spring Lever 



Holes 



^^ 



1.0 3.0 



■».s * 



Steel Band (E) 



steel Band (E) 




Attach strip (C) vertically 
to the adjacent corner of the 
base, Glue a strip of white 
paper (D) to the top front 
surface of strip (C) to serve 
as a scale. 

Take packing case steel band 
(E) and make a small V-shape 
at one end to hold the scale 
pan support wire. Drill two 
holes in the other end to 
V-Shaped Support take two small nails. 

Attach the drilled end of 
band (E) to the top of block 
(B) on the base with two small 
nails. Bend the band smoothly 
over to form an elongated 
C-shape as indicated. 



^y 



Strip (C)' 



Wood (B) Base (A) 



(4) Scale Pan 




[■*- 



12 .5 



-Q 




Take the galvanized iron wire 
(F) and make it into a double 
strand 25 cm long. Use half 
of the new length to form a 
"figure 8" in the wire. 



Galvanized Wire (F) 




1.0 4.0 



-H 



Scale Pan 
Support (F) 



Fold one loop on top of the 
other, and then bend the 
remaining straight portion of 
the wire to the shape indicated. 
You now have a scale pan support 
which may be attached to the 
spring lever. 




Masses 



c. Notes 



Make the pan itself from the 
aluminum sheet (G) . Hammer 
it at the center to create a 
saucer shaped pan. Sit the 
pan on the loop of the scale 
pan support. 

Such items as nails, washers 
and paper clips may be used 
for masses, 



(i) Note the point of intersection between the spring lever and the left side 
of the scale, and record the position with a temporary zero mark. Determine 
the elastic limit of the spring lever by adding successively larger masses to the 
scale pan, and noting on each occasion whether the spring returned to the same 
zero point on removing the masses from the pan. In this particular case it was 
noted that the elastic limit was reached with a mass of 33 g. 

(ii) Note the new zero point on the scale with a permanent mark. This will be 
slightly below the temporary mark due to the spring being subjected to a force 
which extended it slightly beyond its elastic limit. Now add masses 1 g at a time 
calibrating the scale accordingly up to 20 g. 

(iii) A more sensitive balance, weighing from to 10 g, may be made in an 
identical fashion by using half the width of packing case band as the spring lever, 
Such a balance made here was found to have an elastic limit of 27 g, and was 
readily calibrated as described above. 



A2 . Rubber Band Balance 




(4) Ma 



sses 



(3) Scale Pan Unit 



(2) Support 



(1) Base 



a. Materials Required 






Components 


Qu 


Items Required 


(1) Base 


1 


Wood (A) 


(2) Support 


: 


Wood Strip (B) 




2 

1 


Screws (C) 
White Paper (D) 




2 


Rubber Bands (I 



Dimensions 

15 cm x 10 cm x 1.5 cm 

4 5 cm x 4 cm x 2 cm 
2.5 cm long 
30 cm x 4 cm 



(3) Scale Pan Unit 



(4) Masses 

b. Construction 

(1) Base 

(2) Support 



Nail (F) 
Rubber Band (G) 
Galvanized Wire (H) 
Aluminum Sheet (I) 
Wire (J) 
Adhesive Tape (K) 

Washers 



Rubber 
Bands (E) 




cztt 



-Suppor 



US) 



White Paper (D) 



Base (A) 



\ 



Screws (C) 



(3) Scale Pan Unit 




Nail (F) 
Tape (K) 

«*— Rubber Band (G) 

Ring (H) 

Support Wires (0) 

Scale Pan (I) 



7 cm long approximately 

#20, 3 cm long 

6 cm x 6 cm x 0.02 cm 

#24, 9 cm long 

10 cm x 1 cm 



Use wood (A) to serve as the 
base. 

Attach wood strip (B) 
vertically to the base with 
two screws (C) . Attach the 
plain white paper (D) to the 
front of the vertical support 
(B) with rubber bands (E) . 



Drive nail (F) horizontally 
into top of the vertical 
support, and suspend a rubber 
band (G) from its end. Take 
the galvanized wire (H) and 
bend it into the shape of a 
ring which can be suspended 
from the rubber band. 

Hammer the aluminum sheet (I) 
at its center so as to create 
a saucer shape, thus producing 
a reasonable scale pan. Use 
a hammer and nail to produce 
three small holes near the 
perimeter of the pan. Suspend 
the pan from the ring by 
means of the three lengths of 
wire (J) bent over at both 
ends to form suitable hooks. 



£==CZ3Pl 



Nail 



-Rubber Band (G) 



Tape (K) 



Masses 



To prevent the rubber band 
sliding backwards and forwards 
on the supporting nail a length 
of adhesive tape (K) should 
be wrapped around the nail so 
as to leave a groove between 
the tape and the end of the 
nail, the rubber band being held 
in position in the groove. 

Such items as nails, washers 
and paper clips may be used 
as masses. 



c. Notes 



(i) Note the point on the scale corresponding to the position of the unloaded 
scale pan. Determine the elastic limit of the rubber band by loading the scale 
pan with increasing masses, noting In each instance whether the unloaded pan 
returns to the same zero point on the scale. For the particular band used in this 
instance the elastic limit was reached with a mass of 235 g. 

(ii) Check the zero position on the scale once more, making a permanent mark 
opposite the scale pan, then calibrate the scale by adding successive weights to 
the pan, keeping well within the elastic limits of the band. 

(iii) A nonuniform scale will result . 

(iv) The rubber band will deteriorate with time, and this will be particularly 
rapid in tropical countries. However, the band can easily be replaced and the 
scale recalibrated so long as the teacher has a suitable set of weights available. 

(v) Ifthe scale pan is suspended from two parallel elastic bands, instead of 
one the range and the elastic limit will be increased. With two bands the elastic 
limit increased in this particular case to 550 g. However, it was noted that if 
masses of less than 500 g were left on the pan for any period of time there was 
still a tendency for the rubber band to be plastically deformed. 



A3. Simple Beam Balance 



^^" 



(1) Balance Arm 



w 



(2) -Pivot 




(3) Masses 



a. Materials Required 

Components 

(1) Balance Arm 

(2) Pivot 

(3) Masses 

b. Construction 

(1) Balance Arm 

(2) Pivot 



Qu Items Required 
1 Meter Ruler (A) 

1 Wood (B) 

Washers (D) 




Dimensions 
100 cm long 

4cmx4cmx2cm 



Use the meter ruler (A) as a 
balance arm. 

Round off one end of the 
available piece of wood (B) 
with sandpaper. 



(3) Masses 



Use washers or heavy nuts (D) 
for masses. 



B. EXPERIMENTAL BALANCES 



Bl. Extending Spri nqBalance 




(2) Spring 



(1) Support 



a. Materials Required 
Components 

(1) Support 

(2) Spring 

b. Construction 
(1) Support 



Qu I tems Required 

1 Rubber Band Balance (A) 



: 



Steel Wire (B) 



Dimensions 
I/A2 

0.09 cm diameter, 
225 cm long 



Make the support (A) in 
precisely the same way as the 
rubber band balance described 



■10- 



(2) Spring 




Taut Wire (B) 




Clamp 



Cork Borer 



amimmwimvamp 



0.1 



End Loop 



Spring (B) 



under I/A2, 

Take a length of steel wire (B) 
(e.g. piano wire) and fasten 
one end firmly in a clamp. 
Attach the other end to a cork 
borer or similar device (see 
notes) . If the diameter of the 
axis of the cork borer used is 
1.4 cm, the diameter of the 
resultant spring (when released) 
will approach 2 cm. Keeping 
the wire under tension wind 
some 30 turns of wire into the 
spring, each turn being 
separated from the next by 
about 0.1 cm. Use pliers to 
twist a loop in each end of 
the spring. Remove the rubber 
band which supports the scale 
pan in the rubber band balance 
(A) , and replace it by the steel 
spring. 



c. Notes 



(i) Determine the elastic limit of the steel spring, and calibrate the balance 
in exactly the same way as for the rubber band balance. 

(ii) With the materials described above the spring was extended until the scale 
pan touched the base of the apparatus without reaching the elastic limit of the 
spring. The scale was calibrated from to 400 g (an extension of 19.6 cm), and 
it was noted that the resultant scale was uniform. 

(iii) A more sensitive, or weaker, spring may be made by using thinner wire or 
by making the diameter of the spring greater, 

(iv) A very convenient winding device for the spring is a wooden dowel (in this 

case 1.4 cm diameter, 30 cm 
If ~*\ long) with a hole (0.6 cm 

diameter) drilled at either 



t 

Nail 




Hole 



Dowel 



end to take a nail about 
10 cm long. 

A small hole (diameter 0.2 cm) 
drilled through the center of 



-li- 



the dowel holds the wire, and the latter may be wound into a spring in much the same 
way as with the help of the cork borer, in this case winding the wire spring onto 
the wooden dowel which is turned with the help of the protruding nails. 



12- 



B2. Compression Spring Balance 




— (5) Scale Pan 



— (4) Upper Platform 



(3) Support Block 



(2) Frame 



(1) Syringe 



a. Materials Reguired 
Components 
(1) Syringe 



(2) Frame 



g u Items Reguired 
1 Syringe (A) 



Modelling Clay (B) 

Wood (C) 
Wood (D) 
Wooden Dowels (E) 



Dimensions 

Column length approxi- 
mately 6.4 cm, internal 
diameter approximately 
1.3 cm 



14 cm x 9 cm x 2 cm 

14 cm x 9 cm x 0.7 cm 

12 cm long, 1 cm 
diameter 



(3) Support Block 



(4) Upper Platform 



Wood (F) 



1 


Wood (G) 


2 


Bolts (H) 


2 


Wing Nuts (I 



2 cm x 2 cm x L cm, 
where L is dependent 
on length of syringe 

14 cm x 9 cm x 0.07 cm 

2 cm long, 0.3 cm 
diameter 

0.3 cm diameter 



-is- 



is) Scale Pan 



b. Construction 
(1) Syringe 




(2) Frame 



1 Galvanized Wire (J) 

1 Aluminum Sheet (K) 
1 Wood (L) 



Flanges Removed 
Plunger 

Col umn 

Lubrication 

Clay Seal (B) 

— Needle Removed 




Column 

Clay Seal (B) 
Needle Holder 




Platform 



(D) 



Dowels (E) 



Base (C) 



32 cm long, 0.4 cm 
diameter 

12 cm x 12 cm x 0.05 cm 

5cmx5cmx2cm 



Take the disposable plastic 
syringe (A) and remove the 
needle and the top flanges. 
Remove the plunger from the 
column, and smear the end 
of the plunger with petroleum 
jelly thus insuring a well 
lubricated plunger, and a 
good airtight seal. 



Insert the plunger about 
1 cm into the column, and 
then seal off the open end 
of the column with modelling 
clay with the help of the 
metal needle holder. 

Make the base of the frame 
from wood (C) drilling holes 
(1 cm diameter) at the corners 
to take the dowels (E) . Use 
wood (D) as a platform, 
drilling holes (1 cm diameter) 
at each corner to take the 
dowels. Attach the base and 
platform together by means of 
the four dowels, fixing the 
latter firmly in position 
with wood cement. Drill a 
hole (1.4 cm diameter) through 
the middle of the platform, 
making it just large enough 
to take the plunger. 



-14- 



(3) Support Block 



L-, 



Syringe Column 



iC 



Support Block (F) 



Upper Platform 




— Bolt Hole 

Platform (G) 
Bolt Hole 

Frame 



Insert the syringe column through 
the hole in the platform. It 
will hang suspended with a gap 
between the bottom of the syringe 
and the surface of the base. 
Cut a small support block (F) 
to fill this gap, and drill a 
small inset into the top of 
the block to hold the syringe 
firmly in position. (The block 
will also prevent the modelling 
clay seal in the bottom of the 
syringe being readily broken 
under pressure) . Fasten the 
support block to the base with 
wood cement . 

Make the upper platform from 
wood (G) to fit on top of the 
existing platform for the frame. 

Drill a hole (diameter the same 
as that of the syringe plunger) 
in the middle of the upper 
platform, and slide the latter 
into position on the frame. 
Drill two bolt holes (0.3 cm 
diameter) through both platforms, 
and fasten them together by 
means of bolts (H) and wing nuts 
(I), thus holding the syringe 
firmly in position. 



15) Scale Pan 




Frame /J) 



Make a frame for the scale pan 
out of aluminum or galvanized 

wire Id), 



-15- 



2.5 




Fold Lines 




Metal Sheet (K) 



Cut the corners (2.5 cm x 2.5 cm) 
out of the aluminum sheet (K) , 
and fold the projections as 
illustrated so that they may be 
bent over the wire frame to 
form a suitable scale pan. 



Wire Frame FoldedPro jection 




Hole 



Block (L) 




Take the wooden block (L) , 
and drill a hole (the same 
diameter as the plunger, and 
1.5 cm deep) into the middle 
of the block. Nail the scale 
pan squarely on to the undrilled 
surface of the block. Line 
the inside of the hole in the 
lower surface with wood filler. 

Lower the block onto the 
plunger. The latter will be 
held firmly within the hole 
once the wood filler dries. 



•16- 



c. Notes 

(i) The balance may readily be calibrated with known weights by noting the length 
of the trapped air column for each given mass in the scale pan. 

(ii) The variation of length of the air column with mass is not linear, as can be 
seen from the plot below showing the relationship of air column length (L) to the 
applied mass (M) . 

M g 



2000 



1500 



1000 



500 




"V Lmm 



L = 


mm 


47 


8 


44 


8 


42 


4 


41 


2 


40 





38 


8 


37 


6 


36 


4 


32 


8 


28 






30 



36 



42 



(iii) Because of friction between the plunger and the sides of the column, the 
syringe tends to be insensitive to weights of less than about 500 g, but it readily 
measures weights from this lower limit up to around 5,000 g. 

(iv) The sensitivity of the balance appears to increase as the 1 ength and diameter 
of the syringe column increases. 

(v) In designing new balances it would be of particular interest to consider the 
use of a syringe as an extension spring, as illustrated in the diagram. It would 

n appear that this balance might 




Syringe 



have guite a different range 
and sensitivity from that of 
the compression spring balance. 



Scale Pan 



-17- 



B3 . Peqboard Balance 

Support Stand 
(1) 




Pivot 
(2) 




(3) Balance Arm 



(4) Hooks 



(5) Masses 



(6) Spring Clips 



a. Materials Required 






Components 


Qu 


Items Required 


(1) Support Stand 


1 


Wood (A) 




1 


Pegboard (B) 


(2) Pivot 


1 


Wood (C) 




1 


Nail (D) 




2 


Bolts (E) 



(3) 


Balance Arm 


1 
1 


(4) 


Hooks 


6 


(5) 


Masses 


20 


(6) 


Spring Clips 


2 



Dimensions 

50 cm x 10 cm x 2 cm 

50 cm x 35 cm x 0.3 cm 

8cmx3cmxlcm 

5 cm long, 0.3 cm 
diameter 

2 cm long, 0.3 cm 
diameter 

Wing Nuts (F) 0.3 cm internal diameter 

Wood (G) 50 cm x 2.5 cm x 0.5 cm 

Aluminum Sheet (H) 2 . 5 cm x 2 . cm x 

0.02 cm 

Paper Clips (I) 

Washers (J) 

Packing Case Steel Bands (K) 8 . 5 cm x 1 cm x . 02 cm 

Bolts (L) 



Wing Nuts (M) 



1.5 cm long, 0.3 cm 
diameter 

0.3 cm internal 
diameter 



b. Construction 

(1) Support Stand 



(2) Pivot 



■"^ 



(5SZ&ZZ 



3 



\ 



Bolt (E) 
Nail (D) Block (C) S Wing Nut (F) 



(3) 



Balance Ann 
Z.Q 



0.5.N.W 
jr 



-*» 



i.o] I 



> — a 



Counterbalance (H) 



0.5 



Counterbalance (H) 



.25 



Balance Arm (G) 



(4) Hooks 



1 
4.0 



Attach the sheet of pegboard (B) 
vertically on to wood (A) to 
make the support. 

Orill a small hole (diameter 
0.2 cm) through wood (C), and 
make a small inset over the 
hole. Drive nail (D) through 
the hole so that the nail head 
sits in the inset. 

Drill two more holes (diameter 
0.3 cm) through the wood, close 
to the edges, and use bolts (E) 
and wing nuts (F) to attach the 
block to the pegboard support 
stand. The newly attached 
pivot nail should be at the 
center of the pegboard and about 
20 cm above the base. 

Make the balance arm out of 
wood (G) . Drill holes (0.5 cm 
diameter) at regular intervals 
in the arm as illustrated, and 
balance the arm as reguired 
on the nail pivot. Take a sheet 
of aluminum (H) and bend it into 
a counterbalance. Set.it in an 
appropriate position on the 
balance arm to correct any 
irregularity in the balance of 
the latter. 

Make each hook by straightening 
out a paper clip (I) , and 
cutting off a length of about 
6 cm. Then bend the wire into 
the shape shown. Make six 
such hooks. 



Hook (I) 



-19- 



'5)Masses 



(6) Spring Clips 




Spring (K) 



C. Notes 



Wing Nut (M) 



Bolt (L) 



Stand (B) 



Use heavy washers (J) or nuts 
for masses. 

Take a length of packing case 
steel band (K) and drill a hole 
(diameter 0.3 cm) through its 
center. Then bend i t as 
indicated into the form of a 
spring clip. This size of 
spring clip is suitable for a 
standard test tube. Attach 
this to the support stand with 
a bolt (L) and wing nut (M) . Two 
identical spring clips should 
be made. 



(i) The position of the pivot in the horizontal lever can be changed at will 
not only from one end of the lever to the other, but also from the lower edge of 
the lever to the upper edge (changing the sensitivity of the balance) . The 
apparatus is particularly suitable for studying "moments". 

(ii) With the help of the spring clips described the apparatus may be converted 
into a general support stand. 




-20- 



Soda Straw Balance 




(3) Masses 



• (2) Balance Arm 



(1) Support 



a. Materials Required 
Components 

(1) Support 

(2) Balance Arm 

(3) Masses 

b. Construction 
(1) Support 



(2) Balance Arm 



Qu I tems Required 

2 Wood (A) 

1 Aluminum Sheet (B) 

1 Soda Straw (C) 
1 Needle P 

10 Paper Clips (E) 





Aluminum Support (B) 



Hole 



"T" Support (A) 



Dimensions 

6cmx2cmx2cm 

6 cm x 2 cm x 0.02 cm 

16 cm long approximately 
3 cm long 



Screw, or nail, one block of 
wood (A) on to the other so as 
to form an inverted sheet (B) 
and bend this into a three 
sided support to sit on top of 
the inverted "T" support. 
Drill a small hole through 
the base of the aluminum sheet 
so that the latter may be 
attached to the wood support 
by means of a nail or screw. 

Pierce the middle of the straw 
(C) with needle (D) making 
sure that the latter is close 



-21- 



\ 



to the top surface of the 
straw, thus lending stability 
to the balance arm. Use a 
razor blade to cut small V- 



SlotS Needle shaped slots in the top 

surface of the straw at regular 
intervals of 2 cm. Balance the 
straw on top of the support. 

(3) Masses Use the paper clips (E) as 

appropriate masses. 

c. Notes 

(i) This apparatus is suitable for individual student investigation of the 
principle of "moments". 



B5. Microbalance 



-22- 




(3) Scale 



(2) Balance Arm 



(1) Support 



a, Materials Required 
Components 
(1) Support 



(2) Balance Arm 



(3) Scale 



Construction 



Qu 

1 

1 
1 




Items Required 
Wood (A) 
Screw (B) 
Aluminum Sheet (C) 

Straw 
Bolt (E) 
Needle (F) 

Wood Strip (G) 
White Paper (H) 
Rubber Bands ) 



Screw (B) 



Aluminum 
Support (C) 



Wood (A) 



Dimensions 

15cmx2cmx2cm 

1 cm long 

6 cm x 2 cm x 0.02 cm 

16 cm long approximately 
1 cm long approximately 
3 an long 

12 cm x 2 cm x 0.4 cm 
10 cmx 2 cm 



Bend the aluminum sheet (C) 
into a three sided support. 
Drill a hole (0.2 cm diameter) 
through the middle of the 
support base, and then attach 
the support to the end of 
wood (A) by means of a screw 



-23- 



(2) Balance Arm 




Scale Pan 



Straw 



through the hole. 

Take the straw (D) and select 
a short bolt (E) which fits 
tightly into the end of the 
straw. Screw the bolt partway 
into the straw. Cut the free 
end of the straw with a pair 
of scissors to make an 
appropriate scale pan in the 
balance arm, Pierce the straw 
near to the top surface, and 
sufficiently close to one end, 
with the needle (F) so that the 
latter will serve as a pivot. 
Balance the straw on the 
support. A few trials will 
be necessary to obtain a 
suitable position for the 
needle. 



(3) Scale 



c. Notes 



Nail the wood strip (G) verti- 
cally on to the end of the 
base (A) , and attach the piece 
of white paper (H) to the 
front surface with rubber bands 
(I). 



(i) The position of the pivot and screw should be adjusted so that the straw 
points toward the top of the scale. Assuming the weight of a large sheet of paper 
(or several sheets together) can be determined, calibration may be effected by 
placing a fraction of a sheet of paper (e.g. 1 square cm or less) on the soda straw 
scale pan, and noting the depression of the straw on the scale. This balance is 
sufficiently sensitive to determine the mass of extremely small bodies such as 
mosquitoes, strands of hair etc. 



-24- 



C. FUNCTIONAL BALANCES 



CI. Equal Arm Balance 



(3) Balance Arm 



(2) Support 




(1) Base 



Scale Pan 



a. Materials Required 
Components 
(1) Base 



(2) Support 



g u Items Required 

1 Softwood (A) 

4 Bolts (B) 

8 Nuts (C) 

1 Screw (D) 

1 Wood (E) 

1 Razor Blade (F) 
(Double Edqe) 



Dimensions 

38 cm x 9 cm x 2 cm 

0.2 cm diameter, 
3 cm long 

0.2 cm internal 
diameter 

3 cm long 

15.5 cm x 3 cm x 2 cm 



© From ReginaMelton, El ementary, Economic Experiments in Physics, Apparatus Guide , 
(London: Center for Educational Development Overseas, 1972), pp 5-8. 



-25- 



(3) Balance Arm 



(4) Scale Pans 



1 Wood (G) 

1 Needle (H) 

1 Aluminum Sheet (I) 

1 Aluminum Sheet (J) 

2 Aluminum Wires (K) 
2 Aluminum Sheets (L) 
1 White Paper (M) 



b. Construction 
(1) Base 




Nut (c) 



Levelling 
/ Bolt (B)" 




Nut (C) 



Side View 



(2) Support 



38 cm x 2 cm x 0.5 cm 

0.1 cm diameter, 5 cm 
long 

19 cm x 0.5 cm x 0.5 cm 

4 cm x 1.5 cm x 0.05 cm 

50 cm long, 0.3 cm 
diameter 

13.5 cm x 13.5 cm 
x 0.02 cm 

4 cm x 2 cm 

Make the base out of softwood 
(A) . Drill four holes (diameter 
0.3 cm) in the base to take the 
four levelling bolts (B) . 
Inset the nuts (C) into the 
base above and below the holes 
by hammering the nuts into the 
wood surface. They may be 
fixed permanently in position 
with epoxy resin. 

Two nuts (C) on each bolt (B) 
prevent the latter from wobbling, 
and permit easy hand adjustment 
of the bolt. 

Bore an additional hole (approx- 
imately 0.2 cm diameter) at the 
center of the base to facilitate 
the attachment of the support. 

Cut the support to the shape 
shown from a piece of wood (E) 
and cut slots approximately 1 cm 
deep in the top surface with a 
saw. Attach the support to the 
base with the screw (D) 
inserted through the hole in 
the center of the base, making 
a strong junction with the help 
of wood cement. Then, cut the 



-26- 



1.0 




Slits 



razor blade (F) in half, and, 
after smearing the cutting 
edges with epoxy resin, insert 
the cutting edges of the blades 
as deep as possible into the 
slits. The less the blades 
protrude above the wood the 
less the strain that is possible 
on the projecting blades. 




Razor 
Blades 



(3) Balance Arm 

Pivot 
Hole 




Notches 



Make the balance arm out of 
softwood (G) , cutting a notch 

(0.5 cm wide, 1.0 cm deep) at 
5. distance of 1.5 cm from each 

end of the arm. 




Pivot 
Needle (H) 



Drill a hole (0.1 cm diameter) 
horizontally through the middle 
of the arm at a distance of 
0.5 cm from the top of the arm. 
Drive the steel needle (H) 
through the hole to serve as 
a pivot, and glue it permanently 
in position with epoxy resin. 



-27- 



0.4 J£ 





Counterbalance 



Counterbalance (J) 

\ 




Pointer (I) 



The needle must be sufficiently 
strong not to bend, even under 
heavy loads. 

Take the sheet of aluminum (I) 
and bend it into the shape of 
a pointer as illustrated. 
Then attach the pointer to the 
middle of the balance arm. 



Complete the balance arm by 
making a small counterbalance 
from the sheet of aluminum (J) , 
bending it to the shape 
indicated. Sit the counter- 
balance on the balance arm. 



(4) Scale Pans 




Take the length of aluminum or 
galvanized wire (K) and bend 
it into a support for the scale 
pan. Make an identical support 
in the same way, and suspend 
both supports from the notches 
in the balance arm, 



-28- 



7.5 



hs 



Scale Pan 
Support 




0.5 

6 



i i 
i 
i i 



i i 



vl H 



7.5- 



■ 0.5 



1.5 



1.0 



Scale Pan 



Cross Section 



Make the scale pan from the sheet 
of aluminum (L) . Cut squares 
(3 cm x 3 cm) from the sheet 
corners to make four projections 
on the sheet, and cut a slit 
in one of the projections as 
indicated. Fold the projections 
along the dotted lines converting 
the aluminum sheet into a scale 
pan with sides. Sit the scale 
pan on the framework of one of 
the support wires. Make a 
second scale pan in an identical 
manner. 




Scale Pan Support 



Scale Pan 



h 3 -H 




Make a small scale from a piece 
of white paper(M.) by marking, 
regular divisions (0.3 cm apart 
approximately) on the paper. 
Glue the scale to the support 
just behind the pointer so that 
when the balance arm is 
perfectly horizontal the pointer 
will be at the middle of the 
scale. 



-29- 



c . hates 

(i) The following table gives approximate values for the sensitivity of such a 
balance under varying loads. Sensitivity is measured as the number of milligrams 
reguired to cause the pointer to move one millimeter under the given load. 



Load in Each Pan 


< 
Sensitivity 


25 g 


25 mg/mm 


50 g 


25 mg/mm 


100 g 


65 mg/mm 


250 g 


200 mg/mm 


500 g 


335 mg/mm 



(ii) As seen in the illustration, the shape of the razor blade edge allows three 

different points to be used 
£ as fulcrums for the pivot 

needle. Sensitivity is found 
to be essentially the same at 
all three points for all 
weights . 

(iii) The centering point of the pointer is very stable under varying weight loads. 
However, if the weights are shifted drastically in position in the pans (that is, off 
center) then shifts in the pointer position of up to 2 mm may be noted. 



-30- 



C2. Box of Masses 



oooo 

o o o o 





(2) Mass 



' (1) Box 



a. Materials Required 

Components 

(1) Masses 

(2) Box 

b. Construction 

(1) Masses 



Qu Items Required 

1-3 Lead (A) (sheetinq, etc.; 

9 Eye Screws (B) 



Dimensions 

2 kg approximately 



: 



Wood (C) 




'.up 



Screw 



17 cm x 8 cm x 5 cm 

Take a box of wet sand, and use 
wooden dowels, or some such 
similar material, to make 
cylindrical molds in the sand 
according to the dimensions 
given below. Heat up some lead 
(A) in a can, and when it is 
molten pour it into the molds . 
Allow the lead to solidify and 
cool. Then screw into the top 
of each lead cylinder a cup 
screw (B) to serve as a handle. 

The lead cylinders may then be 
filed down until each is the 
desired mass. The number of 
masses required, and the 



©From Reginald F. Melton, Elementary, lecon 
(London: Center for Educational Development 



omic Experiments in Physics, Apparatus Guid e, 

Overseas, 1972) PP 9 _ 10 . 



-31 



approximate size of each mold, 
is indicated below. 



Qu 

1 

3 

1 
1 
2 

1 



Weight 


Diameter 


Depth 


500 g 


3.8 cm 


4.0 cm 


200 


2.4 


4.0 


100 


2.4 


2.0 


50 


2.4 


1.0 


20 


1.2 


2.0 


10 


1.2 


1.0 



(2) Box 



Take the block of wood (C) and 
drill holes, the same size as 
the above molds, into the top 
surface. These will serve as 
suitable mass holders. 



-32- 



C3. Single Pan Balance 




a. Materials Required 
Components 
(1) Base 

( 2 ) Support 

(3) Balance Arm 



(4) Scale Pan 

(5) Counterbalances 



b. Construction 



(2) Support 



q u Items Required 

Equal Arm Balance Base (A) 

Equal Arm Balance 
Support (B) 

Soft Wood (C) 
Needle (D) 
Aluminum Sheet (E) 



Dimensions 
I/ClComponent (1) 

I/ClComponent (2) 

4 2 cm x 2 cm x . 5 cm 

5 cm long 

19 cm x 0.5 cm x 0.05 cm 



Equal Arm Balance Scale Pan 1/CJ.Component (4) 

Washers (F) 
Washers (G) 
Paper Clips (H) 



Approximately 70 g total 
Approximately 12 g total 



(1) Base 



Make the base (Component 1) of 
the Equal Arm Balance (I/Cl) 
and use it as the base (A) of 



-33- 



(2) Support 



(3) Balance Arm 



Hole /, 



\ h-*t 



Needle (D) 



A 



0.5 1+ 8.5 -I 



0.5 




14 



y 



>> 



31 



of this item. 

Make the support (Component 2) 
of the Equal Arm Balance (I/Cl) 
and use it as the support (B) 
of this item. 

Make the balance arm from the 
soft wood (C) . Drive the needle 
(D) horizontally through the 
arm 9 cm from one end and . 5 cm 
from the top surface. Cut a 
notch (0.5 cm wide, 1 . cm deep) 
in the top of the arm and drill 
a small hole (0.2 cm diameter) 
through the corner of the wood. 

Take a sheet of aluminum (E) 
and bend it into the shape of 
a pointer as illustrated. Then 
attach the pointer to the arm 
just above the pivot. 

Sit the balance arm on top of 
the support so that the needle 
serves as a pivot. 



(3) Scale Pan 



(4) Counterbalance 



Make the scale pan (Component 4) 
of the Equal Arm Balance (I/Cl) , 
and suspend it from the notch 
in the balance arm. 

If it is desired to use the 
balance to weigh the masses up 
to 300 g, a standard 300 g 
mass should be placed in the 
scale pan and washers (F) should 
be suspended from a paper clip 
(H) to make counterbalance (I) . 



-34- 



Scale 



Washers (F) 




r-rr 



T I T 



3 



*^— Paper Clip (H) Has(|ers (G) 



Counter- 
balance II 



Counter- 
balance I 



Side View 



The latter should be such that 
when it is suspended from the 
end of the balance arm (position 
Z) it will just balance the 
300 g mass. (In this particular 
instance two washers weighing 
a total of 70 g were found to 
be ideal.) 

The counterbalance should then 
be moved to a suitable zero 
position (Y) on the arm. The 
balance arm will not remain 
horizontal. Therefore make a 
second counterbalance II from 
the small washers (G) such that 
when these are suspended from 
the end of the arm (position X) 
they will just balance the arm 
in a horizontal position with 
counterbalance I in the zero 
position (Y) . (In this instance 
washers weighing a total of 12 g 
made a suitable counter- 
balance II). 

You are now ready to calibrate 
the scale. Stick a piece of 
paper to the balance arm with 
adhesive tape to facilitate 
the marking of the scale. Then 
place standard masses (50, 100, 
150, 200, 250, 300 g) in the 
scale pan, and in each instance 
determine the position of the 
counterbalance (I) which balances 
the arm. A uniform scale should 
be created, and this may be 
subdivided as desired. 



-35- 



c . Notes 

(i) Alternative scales may be produced in an identical manner simply by altering 
the magnitude of counterbalance I (leaving the mass of counterbalance II the same 
as before) . For example using only one washer (35 g) for counterbalance I a scale 
from to 140 g was created on the same balance. 



C4. Spring Balance 



© 



-36- 




Spring 



(3) Outer Tube 



a. Materials Required 










Components 


Qu 


Items Required 




Dimensions 


(1) Spring 


1 


Roll of Steel Wire 


(A) 


#26 gauge (for 
10 Newton Balance) 




1 


Roll of Steel Wire 


(B) 


#30 gauge (for 
1 Newton Balance) 


(2) Inner Tube 


1 


Hollow Aluminum Tube (C) 


21 cm long, internal 
diameter 1 cm 




2 


Wood Stoppers (D) 




1 cm diameter, 2 cm 
long 




1 


Cup Screw (E) 




-- 


(3) Outer Tube 


1 


Hollow Aluminum Tube (F) 


27 cm long, internal 
diameter 1.3 cm 




1 


Wood Stopper (G) 




1.3 cm diameter, 2 cm 
long 




2 


Cup Screws (H) 




— 


b. Construction 











(1) Spring 



The most important factor in 
winding a spring is to keep 
the wire taut at all times, 
and for this the help of a 



©From Reginald F. Melton, Elementary, Economic Experime nts in Physics, Apparatus Guide, 
(London: Center for Educational Development Overseas, 19)2), pp 31-33. 



-37- 




Free Moving 
Nail 



Fixed Nail 



Brace 



I r 




Straight 



Spring 



brace and two nails (10 cm long, 
0.7 cm diameter) is invaluable. 
Drill a horizontal hole about 
3 cm deep in the bench for the 
free moving nail, and about 
20 cm to the right of this drive 
in a second (fixed) nail. Clamp 
one end of the wire (A/B) along 
with the head of the free nail 
in the jaws of the brace, and 
get your partner to hold the 
other end of the wire in the 
jaws of a pair of pliers, 
keeping the wire taut with the 
assistance of the fixed nail. 
Turn the brace, winding the wire 
firmly around the free nail, 
The spring may be close wound 
(each turn touching the next) 
or open wound (each turn 
separated from the next by a 
fixed distance) . Although 
the wire is wound on a nail 
of diameter 0.7 cm, on release 
from tension it will tend to 
expand to about 1 cm diameter. 

Ifa Newton balance is to be 
made take the #26 gauge steel 
wire (A) (diameter 0.07 cm) 
and open wind it (0.1 cm 
between each turn) into a spring 
approximately 8 cm long and 
0.9 cm in diameter. 

Make a loop on one end of the 
spring (using dog nosed pliers) 
and a straight piece on the 
other end. 



Loop 



-38- 



(2) Inner Tube 





Spring (A/B) 
Stopper (D) 



Inner Tube (C) 
Stopper (D) 

Cup Screw (E) 



Cross Section View 



(3) Outer Tube 



z 



Tube (C) 



HimffomM 



Stopper (G) 
i 



Make two stoppers out of the 
wood (D) . Fix a cup screw (E) 
into one of the stoppers and 
glue it permanently into one 
end of the aluminum tube (C) . 
Drill a small central hole 
through the other stopper (D) 
and insert the straight end 
of the spring, bending the 
end over to hold it in position. 
Glue the stopper into the other 
end of the tube. 

Make a wooden stopper (G) to 
fit one end of the hollow 
aluminum tube (F) . Fix cup 
screws (H) in either end of 
the stopper, and attach the 
top of the spring to one of the 
cup screws, 

Now take the combination of 
stopper, spring and inner tube, 
and lower it into the outer 
tube (F) until the stopper 
lodges in the top of the tube. 
Glue the stopper firmly into 
the tube. 

C .Notes 

(i) To calibrate the 10 Newton spring, hold the balance vertically, and mark the 
inner tube opposite the lower end of the external tube (10 Newtons) . Suspend 
1,020 g from the spring and once again mark the inner tube opposite the lower end 
of the external tube. Then subdivide the distance between the two marks into 100 
equal divisions, thus permitting the balance to read from 0.0 to 10.0 Newtons with 
an accuracy of 0.1 Newtons. 

(ii) To calibrate the 1 Newton spring simply suspend a mass of 102 g from the 
balance and repeat the above process, calibrating the inner tube from 0.00 to 1.00 
Newtons with an accuracy of 0.01 Newtons. 

(iii) Spring balances are very easily damaged by over extension of the spring. It 
is therefore useful to make some simple device to prevent over stressing the spring. 



Spring 



Detail 




Cup Screws (H) 



■39- 



One such method is to tie a piece of magnet wire (diameter 0.05 cm) around 
the inner cylinder, just above the final marking on the scale, If the lower 
perimeter of the outer tube is then tapped gently all around it, the magnet wire 
will be unable to move beyond this point, thus preventing over extension of the 
spring. 



oc 



' ' '- ^U Mmitmmit^ ,' -'■ 



/ 



"\ 



wmmw&wmwvjzs 



Magnet Wire 



Outer Tube 
Tapped Slightly In 



Cross Section 



I 



*r 



■40 



I I . TIMING DEVICES 

Timing devices have been divided into three groups according to the length of time 
intervals they would most conveniently measure. This categorization is somewhat arbi- 
trary, and it follows that some devices could, under certain circumstances, exist in 
more than one category. The categories are defined as follows: 



A. LONG INTERVAL TIMERS 

The intervals to be measured may range from a day (month, year) down to an hour or 
minute . 

B. MEDIUM INTERVAL TIMERS 



The intervals; to b measured would range from minutes to seconds. 
C. SHORT INTERVAL TIMERS 

The intervals to be measured are subdivisions of a second. 



-41- 



A. LONG INTERVAL TIMERS 



Al. Sun Dial 



True North 




— (1) Base 



a. Materials Required 
Components 

(1) Base 

(2) Gnomon 

b. Construction 
(1) Base 



Qu I temg^equired 
1 Wood (A) 



1 



Metal Sheet (B) 




Dimensions 

16 cm x 16 cm x 2 cm 

10 cm x 8 cm x 0.1 cm 

Cut the base from the wood (A) . 
Use a felt pen to mark off the 
surface of the base into four 
equal portions. Draw a circle 
(diameter 7 cm) on the base 
with its center at the middle 
of the base. 



Gnomon 
Position 



-42- 



(2) Gnomon 



Cut Away 
Portion 




Make the gnomon from the metal 
shefe (B) . Bend the end of the 
sheet at right angles to the 
sheet so as to form a base 
piece 1 cm wide. Drill two 
screw holes in the base piece. 
Note the latitude of your local- 
ity (e.g., 39° in Washington, 
D.C.) and markaout right- 
angled triangle on the vertical 
portion of-the metal sheet such 
that the sloping side of the 
triangle is inclined to its 
base at an angle equal to the 
latitude angle. Cut off the 
sheet above the sloping side. 
You now have a metal gnomon. 
Attach the gnomon to the base 
with screws. 



c. Notes 



(i) The base of the apparatus should be placed on a horizontal surface with the 
plane of the gnomon in a true North-South plane, thus making the sloping side of 
the gnomon parallel to the Earth's axis. Calibrate the sun dial against a clock, 
marking in the positions of the shadow with a felt pen or paint. 

(i)i At the North and South Poles the shadow wilil move throug 15° every hour. 
Elsewhere the angle rotated per hour wiM be greater tha 15° in the early morning 
and late evening, andi less tha 15 "towards midday. 

(iii) Since the rotation of the Earth is not exactly 24 hours, the sun will not 
appear to be due North (or South, as the case may be) at noon, Greenwich Mean Time. 
Each month it will therefore be noted that the sun dial deviates further and 
further from the conventional time. From 5 to 30 minutes deviation will be noted 
over a period of one month, depending on the season. 

(iv) The apparent motion of the sun may be used in even simpler (but cruder) 
ways to record the passage of time. It is thus possible to note the motion of a 
spot of sunlight due to a ray of light passing through a hole in a roof, or due to 
a ray of light reflected from a mirror placed by a window. The distance moved by 
the sunspot in successive intervals of time on the same day will be noted to be 
surprisingly regular. (See sketches on next page.) 



-43- 




Sunspot 



Shadow of 
Roof 



Mirror 




Sunspot 



A2 . Water Clock 



-44- 



(4) Pointer System 




(3) Platform 



a. Materials Required 

Components q u 

(1) Upper Reservoir 1 

(2) Lower Reservoir 1 

(3) Platform 1 



(4) Pointer System 



Items Required 
Can (A) 

Can (B) 

Plywod (C) 



3 Wood (D) 

1 Wooden Dowel (E) 

1 Wood Strip (F) 

1 Nail (G) 

4 Washers (H) 
1 Wood (I) 

1 Strigi (J) 

1 Eye Screw (K) 



Dimensions 

1 liter capacity 

1 liter capacity 

50 cm x 15 cm x 1.0 
cm 

20 cm x 3 cm x 3 cm 

B cm lonq, 2 . 5 cm 
diameter 

35 cm x 0.6 cm x 0.4 
cm 

0.2 cm diameter, 
4 cm lonq 

4cmx4cmxlcm 



-45- 



(5) Scale 



b. Construction 



1 Plywod (L) 
1 Wood (M) 

White Paper (N) 



(1) Upper Reservoir 



Bottom 

of Can (A) 




Hole 



(2) Lower Reservoir 



(3) Platform 




Legs (D) 



40 cm x 30 ai x 0.5 cm 
30cmx3 cmx3an 
30 cm x 40 cm 

Take ten tin can (A) and drill 
a small hole (0.1 cm diameter 
for example) in the middle of 
the base. 

The bigger the can, and the 
smaller the hole, the greater 
will be the period of time for 
which the clock will run. This 
may be checked now by filling 
the can with water, and noting 
the time for it to drain. 

If you wish to measure small 
intervals of time, you may 
increase the number of holes 
in the base of the can. 

Use can (B) which should be of 
the same size as, or larger 
than, the can used for the 
upper reservoir. 

Take plywood (C) to make the 
platform, balancing this on the 
three ieg (D) which should be 
sufficiently long to permit the 
lower reservoir to be moved under 
the platform without difficulty. 
Drill a hole (1 cm diameter) in 
one end of the platform. Place 
the upper reservoir over the 
hole in the platform and the 
lower reservoir underneath it so 
that water can run from the 
upper to lower reservoir. 



-46- 



(4) Pointer System 



Upper 
Notch 



Hole 




Make a support from a wooden 
dowel (E) as indicated. Cut a 
lower notch in the support to 
enable it to sit on the side of 
the upper reservoir (A) . Make 
an upper notch to permit the 
full movement of the pointer (E) 
to be attached. Drill a hole 
(0.2 cm diameter) horizontally 
through the upper part of the 
support to permit passage of 
the nai (G) to serve as the 
pivot for the lever. 



Notch 



C J 



:«± 



0.8 



Counterbalance Pivot Hole 
Hole 



Washers 



Pointer (F) 




5> 



Can (A) Wall 



Count erbalaeic 



Make the pointer from a strip 
of wood, (F) . Drill a small 
hole (0.3 cm diameter) at one 
end of the pointer to take the 
string (J) from the counter- 
balance, and 8 cm away from this 
hole drill a second hole (0.3 cm 
diameter) , close to the top 
surface of the pointer, through 
which the nail (G) is to be put 
as a pivot. 

Balance the pointer on the newly 
made support by inserting the 
nail (G) through the appropriate 
holes in the support and pointer. 
Washers (H) should be placed 
either side of the pointer to 
serve as spacers. These prevent 
unwanted motion of the pointer 
on the pivot. The pivot may be 
fixed permanently in position in 
the support with the help of 
epoxy resin, since the pointer 
can move about the fixed axle on 
its own pivot hole. 



-47- 



Scale 




Base Block (M) 




Take the small block of wood (I) 
and attach it to the pointer by 
means of the cptrin (J) and a 
screw (K) attached to the top of 
the block. 

Attach a sheet ofoplywoo (L) 
to the block aif woo (M) 
intended to hold the plywood in 
a vertical position. Sit the 
newly made scale on the platform 
just behind the end of the 
pointer, sufficiently close to 
Plywood (L) avoid parallax problems in 

recording the movement of the 
pointer. Screw the base block 
(M) of the scale onto the plat- 
form. Use a white sheet of 
paper (N) attached to the sur- 
face of the plywood with 
thumbtacks to actually record a 
time scale. 

Adjust the length of string (J) 
on the counterbalance so that 

when the upper reservoir is 
full of water the pointer will 
be set towards the bottom edge 
of the scale. 



c. Notes 

(i) The counterbalance should be wet all over prior to use so that it does not 
tend to sink deeper into the water as it is used. 

(ii) The water clock may be calibrated against a watch. The scale produced will 
not be linear since the water pressure over the hole in the base of the upper 
reservoir decreases as the water level drops. The initial rate of fall of water 
level is therefore greater than the final rate. 

(iii) The clock will be found to be surprisingly reliable, observations being 
guite repeatable. 



-48- 



(iv) Using an upper reservoir of 1.3 liters, a depth of 19 cm and a base hole 
0.15 cm diameter, a five-minute scale was very conveniently created. When the 
number of holes in the base was doubled the pointer traversed the scale in half 
the time (2 ftin 3 sec) ,and when the number of holes was increased to three the 
pointer traversed the scale in one third of the original time (i.e., in 1 min 40 
sec). 



-49- 



MEDIUM INTERVAL TIMERS 



31. Pulse 




(1) Pulse 



a. Materials Required 
Components 

(1) Pulses 

b. Construction 
(1) Pulse 



Qu I tems Required 



C. Notes 



Dimensions 



Place two fingers from the left 
hand over the pulse on the right 
wrist. The pulse beat can 
easily be detected. 



(i) The pulse beat may be calibrated against that of other individuals and 
against other timing devices. Under normal conditions it remains surprisingly 
constant, but its rate varies according to the degree of exertion to which the 
individual is currently subjected. 

(ii) It is useful to note that if the pulse in the neck, just below the angle 
of the jaw, is monitored with one hand, the other hand is left free for other 
functions . 



B2 . Simple Pendulum 



-50- 




(2) Mass 



a. Materials Required 
Components 

(1) String 

(2) Mass 

(3) Support 

b. Construction 
(1) String 



(2) Mass 



Qu I tems Required 
1 String (A) 

1 Paper Clip (B) 

10 Washers (C) 

2 Nais (D) 



Dimensions 
1 meter long 



3 cm long 

Take the length of string (A) , 
and attach a hook [made from the 
paper clip (B) ] to one end. 

Suspend washser (C) from the 
hook to serve as a variable 



(3) Support 



Drive two nails (D) into the side 
of a table, or into a wall, so 
that the nails are at the same 
height above the ground. Wrap 
the desired length of string 
two or three times around one 
nail, and fasten the spare 
length of string to the other 
nail. This should insure that 



-51- 



the string is pivoted rigidly 
at the first nail. 



c. Notes 



(i) If the length of the pendulum, from the support to the center of gravity of 
of the mass, is adjusted t 25 cm (or more accurately to 24.8 cm) the pendulum 
will oscillate with a period of one second. 



-52- 



B3 . Classroom Clock' 



(1) Pendulum *• 

Rod 




(3) Support 
(Not shown) 



(2) Mass 



a. Materials Required 
Components 
(1) Pendulum Rod 



(2) Mass 



QU I tems Required 
1 Broom Handle (A) 

1 Metal Tube (B) 



Nail (C) 



2 


Wood (D) 


2 


Wood (E) 


1 


Wood (F) 


1 


Nail (G) 



Dimensions 

120 cm lonq, 2.5 cm 
diameter 

2.5 cm long, 1 cm 
external diameter; 
approximately 0.7 cm 
internal diameter 

15 cm long, 0.5 cm 
diameter 

22 cm x 6 cm x . 5 cm 

30 cm x 6 cmx 0.5 cm 

31 cm x 22 cm x 0.5 cm 

10 cm long, 0.5 cm 
diameter 



Bricks, Rocks, etc. (H) 



*Adapted from Nuffield Foundation. Guide to Experiments I. Physic s. (London: 

Longmans/Penguin, 1967), pp 79431. 



-53- 



(3) Support 



b. Construction 

(1) Pendulum Rod 



Tables (I) 
Stocsl (J) 



» o a o o o 



1.5 4 



_2_U 

T 

1.5 




Make the pendulum rod out of 
the broom handle (A) . Drill 
six holes (0.6 cm diameter) in 
one end of the rod at 4 cm 
intervals. Drill another hole 
(1 cm diameter) 1.5 cm from the 
other end of the rod. Line this 
with a short length of metal 
tubing (B) to reduce friction 
at the pivot, and insert a long 
nail (C) through the tube. 

Construct a wooden tray to hold 
the masses. Use one paec (F) 
for the base. Nail the four 
other pieces (D,E) to the base 
as shown. Drill a hole (2.7 cm 
diameter) in the middle of the 
tray base (F) , and slide the 
tray onto the pendulum rod by 
way of this hole. Insert the 
strong nail (G) through one of 
the six holes in the end of the 
rod to hold the tray in posi- 
tion. The bricks orsrock (H) 
may be placed ri. the tray tO 
serve as appropriate masses. 



(3) Support 




StocsL (J) 



Tables (I) 



Place two tables (I) fairly 
close together, and sit the 
stools (J) on top of both 
tables, sufficiently close to 
one another so that the pendulum 
may be supported by means of its 
pivot nail resting between the 
tops of the stools. The nail 
(G) must be held firmly in 
position on top of the stools 
hand, clamps, or any device 
which will hold it firmly. 



C. Notes 

(i) With the length (L) of the pendulum from pivot to tray bottom fixed at 
103.5 cm the period (T) of the pendulum was noted to be two seconds. 



Mass = 


7,000 g 


L 


T 


(cm) 


(sec) 


97.0 


1.94 


101.0 


1.98 


105.0 


2.02 


109.0 


2.05 


113.0 


2.09 


117.0 


2.12 



(ii) The initial displacement of the pendulum mass has negligible effect on the 
period. Keeping the length of the pendulum fixed at 105 cm and the mass constant 
at 7,000 g the following correlation of periafc (T) and initial displacemen (D) 
was recorded. 



D 
(cm) 


T 
(sec) 


5 
10 
15 
20 


1.99 
2.01 
2.00 

2.00 



-55- 



(iii) The period of the swing is virtually unaffected by variation of the mass. 
Hence, keeping the pendulum length constant at 105 cm, the mass (M) in the pendulum 
tray was varied by increasing the number of bricks. The following observations of 
the period (T) were recorded. 



M 
(i?) 


T 
(sec) 


1500 


2.00 


3250 


2.00 


5000 


2.00 


7000 


2.01 



(iv) The major effect of increasing the mass (M) of the bricks carried by the 
pendulum is to reduce the damping effect on the oscillations. With the length of 
the pendulum fixed at 105 cm, the pendulum mass was displaced a fixed distance 
(10 cm) and the number of oscillations (N) recorded as the displacement fell from 
10 to 5 cm. The following results were obtained. 



M 
(R) 


N 


Damping Effect 





51.0 


High 


1500 


95.5 


Moderate 


3250 


97.8 


Moderate 


5000 


98.2 


Moderate 


7000 


.1 31 , 6 


Low 



(v)fl this timing device is to be used by a large class, it might be useful to 
modify it slightly to make the counting of oscillations possible without continuous 
visual observation. It is suggested that a metal container might be attached to 
the top of the pendulum rod, and a 2.5 cm ball bearing allowed to roll freely in 
the container, so that a click will occur twice per oscillation as the ball bearing 
hits the ends of the can. 



Can 



Pivot 




BalL Bearing 
(inside can ) 



© 



CI. Ticker Tape Timer 



(2) Vertical 

Support 



-56- 



C. SHOR T INTERVAL TIMERS 



(I) Vibrator 

Unit 




(4) Platform 



a. Materials Required 
Components 

(1) Vibrator Unit 

(2) Vertical Support 1 

(3) Base 1 

2 

(4) Platform 



q u Items Required 

1 Household Electric Bell (A) 

Wood (B) 

Wood (C) 
Screvs (D) 

1 Wood (E) 

2 Aluminum Sheet (F) 
1 Carbon Paps (G) 

5 Thumbtacte (H) 



Dimensions 

7cmx5cmx2cm 

16cmx6cmx2cm 

3 cm lonq 

6cmx5cmx2 cm 
6 cmx 5 cm x 0.05 cm 

4 c m x 4 c m 



<s> From ReginalEL Melton, Elementary, Economic Experiments in Physics, Apparatus 
(guILde,n don: Center for Educational Development Overseas 1972), pp 12-14. 



-57- 



b. Construction 

(1) Vibrator Unit 

Base of Electric Bell 




Bell 



Take the household electric bell 
(A) , and remove the vibrator 
unit. (The bell utilized in 
this instance was designed to 
operate normally at 10 volts.) 



Vibrator Unit 



(2) Vertical Support 



(3) Base 



Holes for Screws 




Space for 
Vertical Support 



Top View 
of Base (C) 



Space for 
Platform 



Use the piece of wood (B) to 
serve as the vertical support, 
and attach the vibrator unit to 
it with screws. 

Use the wood $>iec (C) as the 
base. Place the vertical 
support on the base in such a 
position that the vibrator arm 
will be parallel to, and 
directly above, the line bi- 
Center secting the length of the base. 
Mark in the position of the 
support, and then drill two 
appropriate holes in the base so 
as to facilitate the attachment 
of the support with the screws 
(D) . 



Line 



(4) Platform 

Guides 




Aluminum (F) 



Ticker Tape 



Vibrator Arm 




Attach the aluminum sidepieces 
(F) to wood (E) with nails to 
parbon Paper (G) make a platform. Then with the 
platform in position on the 
base, bend the sidepieces at the 
bottom to hold the platform 
firmly in contact with the base. 
(A loosely fitting platform 
will result in a poor track 
being recorded on the ticker 
tape. ) 

Cut a circular disc out of the 
carbon paper (G) and pierce the 
center so that it may pivot 
freely about a thikmbtac (H) in 
the center of the platform. 

Pin four more thumbtack (H) in 
the platform to serve as guides 
for the ticker tape, which must 
pass under the carbon disc. 
There must be negligible 
friction between the guides and 
ticker tape. 

Bend the vibrator arm downwards 
so thateth endpiece is within 
0.3 or 0.4 cm of the platform 
surface. 



Side View 



c . Notes 

(i) Two dry cells in series will generally operate the timer, even though the 
bell is designed for operation on a 10 volt supply. 

(i)i If ticker tape is difficult to obtain, cashiers' paper rolls (for cash 
registers) are generally available, and may be cut into strips of suitable width, 
so long as care is taken to obtain smooth straight edges. 



-59- 



(i)Li Ifthe ticker tape from the vibrating timer is attached to a moving object, 
the motion of the object will be recorded on the ticker tape. It is thus possible 
to determine the distance moved by the object during specific time intervals. This 
is the basis of a wide range of experiments to determine the relationship between 
force and motion. 



60- 



III. CARTS 

A. FORCE AND MOTION CARTS 

The carts described in this section are presented in increasing order of 
sophistication, ranging from the simplest cart which can only be used for qualitative 
observation to the more sophisticated carts which can be used for quantitative 
experimentation of the relationship between force, mass and acceleration. 



-61- 



A, FORCE AND MOTION CARTS 



Al . Elementary Cart 



(4) Spring 

(Removable) 




(1) Body 



(3) Balloon Support 
(Removable) 



(2) Wheel 



a. Materials Required 
Components 

(1) Body 

(2) Wheels 



(3) Balloon Support 



(4) Spring 



q u Items Required 

1 Cardboard Sheet (A) 

2 Wooden Spools (B) 

2 Coat Hanger Wire (C) 

1 Drinking Straw (D) 

1 Cardboard Sheet (E) 

1 Balloon (F) 

1 Packing Case Band (G) 

1 Washer (H) 



Dimensions 
15 cm x 14 cm 

Diameter of spool ends 
approximately 4 cm 

8 cm long, 0.2 cm 
diameter 



4 cm x 7 cm 



11 cm long, approxi- 
mately 1.2 cm wide 

Approximately 17 g 



* Adapted from Nick Oddo and Edward Carini, Exploring Motion, An Exploring Science 
30k, (USA: Holt, Rinehart and Winston Inc., 1964), pp 24-27. 



-62- 



b. Construction 



(1) Body 



1.0' 




Draw dotted lines on the piece 
of sturdy cardboard (A) and 
make four slits and four axle 
holes as illustrated in the 
diagram. Fold the cardboard 
along the dotted lines to make 
a box, fastening the free sides 
together with the help of 
adhesive tape. 



Cardboard (A) 



(2) Wheels 




Cart Body 



Slits 



Cut four equal sections (each 
1 cm long) from a standard 
drinking straw (D) . Place each 
section into an axle hole in 
the body of the cart, and glue 
firmly in position. The straw 
sections act as bearings for 
the axles as well as spacers 
between the wheels and the body 
of the cart. 



=3= 



\ 



CartBody Straw (D) 

Cross Section 



-63- 




Cut He 



Cut the four wheels from the 
ends of the two wooden spools 
(B) . Fill the spool holes (0.5 
cm diameter) with wood putty 
and allow the putty to dry hard. 



Wheel 



New 
Hole 




Wood Putty in 
Original Hole 



Wheel 



Cut two lengths of wire (C) 

from wire coat hangers to serve 
as axles for the cart. 

Drill holes, slightly less than 
0.2 cm in diameter, through 

the exact center of each wheel, 
and put a little epoxy resin in 
the holes. 



i . — i 



r 



- Axle (C) 

- Cart Body 

Straw (D) 
Wheel 



Tap the end of one axle into one 
of these holes, checking care- 
fully to insure that the axle 
is at right angles (90") to the 
wheel, thus avoiding subseguent 
wheel wobble. 

Insert the axle through the body 
of the cart, and attach a second 
wheel by the same process. Re- 
peat the procedure with the 
remaining two wheels and axle, 
thus providing the cart with 
front and rear wheels. 



-64- 



(3) Balloon Support 




Cut the strong cardboard (E) to 
a "T" shape as shown. Make a 
hole (diameter 1 cm) in the 
center of the top portion. 
Insert the support through the 
pair of slits closest to the 
end of the cart body. Use a 
rubber balloon (F) to provide 
acceleration for the cart [see 
Note (i)]. 



Cardboard (E) 



(4) Spring 




Spring 



Washdr (H) 







Cut the packing case band (G) 
as indicated to make the spring. 
To facilitate the throwing of 
the washers (H) by the spring, 
bend the top end of the packing 
case band at an angle. Insert 
the spring through the remain- 
ing slits in the cart. 



65- 



c , Notes 

(i) Spherical balloons, as opposed to sausage-shaped ones, may be held in the 
balloon support (so long as the spring is removed) , and are capable of accelerating 

the cart by the expulsion of 



Good 
Position 




Bad 
Position 



"0= 

03 




air. The cart will be acceler- 
ated most efficiently if the 
open end of the balloon is held 
in such a way as to prevent it 
flopping from side to side with 
resultant dissipation of energy 
in all directions. 

Not only does the cart motion 
illustrate action and reaction, 
but it also demonstrates 

accelerated motion due to a force. Once the balloon is deflated the acceleration 

ceases and the cart decelerates to a stop. 

(ii) Take a length of strong thread (say 15 cm long) , and tie the top end of the 
spring to the end of the cart in such a way that the top end of the spring is 
almost horizontal. Place a washer on the top end of the spring. If a burning 

Washer 



CP 



Thread 



Spring 




match is applied to the thread, the spring will be released and eject the washer 
forward, while the cart will be propelled backwards, thus offering another demon- 
stration of action and reaction. 



A2 . Lightweight Cart 



(1) Body 



(2) Spring 
Device 




(3) Spring Release 
System 



(4) Ticker Tape 
Bracket 



(6) Wheel System 



a. Materials Reguired 
Components 

(1) Body 

(2) Spring Device 



(3) Spring Release 
System 



Qu I tems Required 
1 Wood (A) 



1 



Steel Wire (B) 



1 Wood Dowel (C) 

1 Rubber Stopper (D) 

1 Screw (E) 

1 Metal Plate (F) 



Dimensions 

15 cm x 6 cm x 5 cm 

80 cm long, 0.09 cm 
diameter 

10 cm long, 1.2 cm 
diameter 

Approximately 2.5 cm 
diameter, and 1.5 cm 
long 

1 cm long 

6 cm x 1.5 cm x 0.05 

cm 



© From Reginald F . Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 1972) , pp 39-46 . 



-67- 



(4) Ticker Tape 
Bracket 



2 


Screws (G) 




1 


Wood Dowel (H) 




1 


Steel Wire (I) 




1 


Aluminum Sheet 


(J) 


2 


Bolts (K) 




2 


Wing Nuts (L) 





(5) Chassis 



(6) Wheel System 



2 Packing Case Steel 

Bands (M) 

2 Wooden Spools (N) 

2 Coat Hanger Wire (0) 

1 Masking Tape (P) 
Washers (Q) 



b. Construction 
(1) Body 




1.5 



Holes for 
Masses 



(2) Spring Device 



1.5 cm long 

3.5 cm long, 0.8 cm 
diameter 

#30, 3.5 cm long 

15 cm x 1.2 cm x 0.05 

cm 

. 2 cm diameter, 2 cm 
long 

0.2 cm internal 
diameter 

Approximately 15 cm x 
1.5 cm x 0.02 cm 

Approximately 4 cm 
diameter 

10 cm long, 0.2 cm 
diameter 

1 cm wide 



Bore a hole from the center of 
one end of wood (A) to the 
center of the other end, in 
order to accommodate a spring 
device. The diameter of the 
hole (1.5 cm) should be 
slightly larger than that of 
the spring (1.2 cm). 

Bore holes into the top surface 
of the wood (A) to accomodate 
six masses (see I/C2), namely 
one 100 g mass (diameter 2.5 cm), 
four 200 g masses (diameter 
2.5 cm) and one 500 g mass 
(diameter 4.0 cm) . The holes 
should not be so deep as to cut 
into the horizontal hole for 
the spring. 

Wind about 60 cm of the steel 
wire (B) into an open spring 
approximately 8.5 cm long, 



o 



Rubber 
Stopper (D) 



Spike 

i 

\ 



Wooden 
Rod (C) 



Spring 



Loop 



1.2 cm in diameter, and with 
about 0.5 cm separation between 
each turn. (A method of winding 
the spring is described under 
I/C4) . Straighten out one end 
of the spring into a spike and 
the other to a horizontal loop. 

Attach the spring of one end of 
the wooden rod (C) by means of 
the spike and epoxy resin. 
Attach the rubber stopper (D) 
to the other end of the rod. 



Screw (E) 




Rubber Wooden 
Stopper (D) Rod (C) 



Spring 



Cross Section 
(Side view) 



Bore a hole into the bottom of 
the cart body so that it meets 
the bore hole for the spring 
3.5 cm from the end of the body. 
Then insert the screw (E) to 
anchor the loop end of the 
spring. 

Ideally, two or three alterna- 
tive springs of varying thick- 
ness and length should be made 
for trial purposes. The 
ultimate spring selected will 
be such that if two identical 
carts (one carrying three times 
its own weight) are placed end 
to end, and the spring device 
on one cart is then released, 
both carts will move apart a 
sufficient distance at uniform 
velocity to enable a measure 
of their initial separation 
velocities to be recorded. 



-69- 



(3) Spring Release System 



Metal Plate (F) 



Cart Body (A) 



Screw 




Hole for 
Spring 



Fasten the metal plate (F) 
(brass, steel, etc.) onto the 
front of the cart with two 
screws (G) so as to just overlap 
the top of the hole for the 
spring. 

File a small notch around the 
wooden rod (C) on the spring 
device, close to the stopper. 

It is thus possible to compress 
the spring into the hole, and 
hold it in position by means 
of the notch and metal plate. 



Rubber 
Stopper (D) 




Notch 



Wooden 
Rod (C) 



Hole for 
Release Rod 



Metal 
Plate (F) 




Bore a vertical hole (diameter 
0.5 cm) into the top of the 
cart, near the front end, so 
that it meets the horizontal 
bore hole for the spring. The 
small wooden rod (H) (release 
rod) inserted into this hole, 
and pressed against the hori- 
zontal rod of the spring device 
itself, will release the spring 
from its state of compression. 
(The need to have the diameter 
of the spring bore hole slightly 



Hole for 

Spring 



Cart Body (a) 



Metal 

Plate (F) 1 



-70- 



Release Rod 




Rubber 
Stopper (D) 



Wooden 
Rod (C) 



Cart 
Body (A) 



greater than that of the spring 
and attached rod should now be 
clear, for it is an essential 
reguirement if the spring is to 
be released) . 



Cross Section 



T 

1.7 



1.7 



Wood Dowel (H) 



-Steel Wire 



(I) 



H 
/ 

0.3 

Release Rod 



(4) Ticker Tape Bracket 





15 




» 






fl 


n n 






i.«- 






II 


t- 




■1' 


\> 4.3- 


--f- 2.8-4— 


-4.3- 


-4H 





Sheet Metal (J) 



Cut the wood dowel (H) to the 
dimensions illustrated. The 
rod should be capable of moving 
freely in its bore hole, but at 
the same time it should not be 
so loose that it is easily lost. 
To prevent losing it, thread a 
thin piece of steel wire (I) 
through the rod so that it acts 
as a spring contact between the 
sides of the rod and the bore 
hole. 

Cut the ticker tape bracket from 
the sheet of metal (J) (brass, 
aluminum) which should be rea- 
sonably rigid, Make slits 
0.5 (0.1 cm wide) near the end to 

i-"* - 0.7 take the ticker tape, and slots 
(0.35 cm wide) along the bottom 

to enable the bracket to be 
attached to the bolts (K) at the 



-71- 



Ticker Tape Bracket 




Bolt (K) 



Cart Body (A) win g Nut (L) 



rear of the cart. Wing nuts 
(L) should be used to fasten 
the bracket in position. 



Cart ] D C Cart 2 




Timer Clamped To T 
Edge of Table 

Mutual Repulsion 



Cart 



<f> 



Timer Clamped To 
Edge of Plane 
On Inclined Plane 



The purpose of the bracket is 
to insure that ticker tape 
attached to the cart is in 
line with the guides of the 
timer during any experiment, 
thus reducing friction. Two 
typical examples are illustrated 
when carts are mutually re- 
pulsed from one another, and 
when a single cart runs down 
an inclined plane. 



(5) Chassis 



Cart Body (A) 




Side View 



Steel Band (M) 



Drill two horizontal holes (0.5 
cm in diameter) through the cart 
body to permit passage of the 
front and rear axles. Make 
these holes 1.0 cm from each 
edge of the cart body (A) . Cut 
the chassis from metal packing 
case bands (M) . Drill five 
holes along the length of the 



-72- 



Axle (0), 



Wheel 




Y////////////A 



Cart 
Body (A) 



strip, two (diameter 0.3 cm) to 
coincide with the centers of 
the axle holes and three to 
enable the strip to be attached 
firmly to the body with screws. 

The axles of the cart will in 
fact pivot in the chassis holes 
and not on the wooden holes 
Chassis (M) through the cart, thus reducing 
friction. 



Cross Section 



(6) Wheel System 




spool (N) 



Cut here 



Cut the four wheels from the 
ends of two wooden spools (N) . 
Fill the spool holes with wood 
putty and allow the putty to 
dry hard. 




Wood Putty in 
Original Hole 



Cut two lengths of wire (0) 
from wire coat hangers to serve 
as axles for the cart. Drill 
holes, slightly less than . 2 cm 
in diameter, through the exact 
center of each wheel, and put a 
little epoxy resin in the holes. 



Wheel 



-73- 




Tape /P). 
Axle (0)- 



y -Cart Body (A) 

W Chassis (M) 

Wheel 



Cross Section 



Tap the end of one axle (0) into 
one of these holes, checking 
carefully to insure that the 
axle is at right angles to the 
wheel (thus avoiding subsequent 
wheel wobble) . 

Insert the axle through the body 
of the cart, and attach a second 
wheel by the same process. 
Repeat the procedure with the 
remaining two wheels and axle, 
thus providing the cart with 
front and rear wheels. 

Make small spacers for all four 
wheels from masking tape (P) , in 
each case wrapping it around 
the axle (next to the wheel) 
until it produces a cylindrical 
spacer 1 cm long and 0.5 cm in 
diameter . 

A little soap applied to each 
axle will serve as a lubricant 
between the axle and chassis 
contact points. 

It is convenient to adjust the 
mass of the completed cart to 
the nearest 100 g. This may be 
done by shaving wood off the top 
or bottom surface of the body of 
the cart, or by adding washers 

to the body of the cart. In 

this case holes were drilled in 
the bottom of the cart, and 
washers (Q) fixed in the holes 
with screws. In this way the 
mass of the cart was adjusted to 
400 g. 



-74- 



c . Notes 

(i) This cart will inevitably be affected by friction more than a cart made 
with ball bearing wheels (III/A3) . However, a full range of force and motion 
experiments may be performed with the cart if an inclined plane is used to com- 
pensate for friction affecting the cart. Simply adjust the inclination of the 
plane prior to any experiment so that the cart runs down the plane with constant 
velocity, the slope of the plane just compensating for the effect of friction. 



-75- 



A3 . Heavyweight Cart 



(2) Spring 
Device 



(1) Body 




(4) Wheel 
System 



(3) Spring Release 
System 



(5) Bumpers 



a.Materials Required 
Components 

(1) Body 

(2) Spring Device 



(3) Spring Release 
System 



(4) Wheel System 



g u Items Required 

1 Wood (A) 

1 Plywood (B) 

1 Wooden Dowel (C) 

1 Roll of Steel Wire (D) 

1 Rubber Stopper (E) 

1 Screw (F) 

1 Aluminum Sheet (G) 

1 Bolt (H) 

2 Nuts (I) 

1 Wooden Strip (J) 

3 Ball Bearing Wheels (K) 

1 Wooden Dowel (L) 

4 Nails (M) 



Dimensions 

30 cm x 8 cm x 4 cm 

30 cm x 8 cm x 0.5 cm 

16 cm long, 1.2 cm 
diameter 

0.09 cm diameter 

Approximately 2 . 5 cm 
diameter 

4 cm long, . 2 cm 
diameter 

8 cm x 3 cm x . 05 cm 

3 cm long, 0.3 cm 
diameter 

0.3 cm internal 
diameter 

8 cm x 2 cm x . 5 cm 

Approximately 

5 cm diameter 

22 cm long, 0.5 cm 
diameter 

Approximately 2 cm long 



(5) Bumpers 



Wood (N) 



12 cm x 2 cm x 2 cm 



-76- 



b. Construction 
(1) Body 



Rear 




Front 



(2) Spring Device 



Rubber Wooden Screw (F) 

Stopper (E) Rod ( C ) Top (B) . 







Notch 



Body (A) Spring 



Cross Section 



Loop 



Cut the body of the cart from 
the piece of wood (A) . Drill 
horizontal holes (diameter D.5 
cm) close to the front and rear 
of the cart to hold the axles 
of the wheel system. 

Using a saw and chisel, cut a 
horizontal slot in the top sur- 
face of the cart to contain the 
spring device, and a vertical 
slot in the rear of the cart to 
accommodate the rear wheel. 

Use the piece of plywood (B) to 
make a top plate for the cart, 
and nail it onto the main body. 

Make the spring device accord- 
ing to the instructions given 
for the previous cart (III/A2) , 
but according to the dimensions 
indicated here. The spring, 
made from the steel wire (D) , 
should be 1.2 cm in diameter and 
16 cm long (excluding the 
spike and loop made on the end 
of the spring) . Nail the rubber 
stopper (E) onto the end of the 
wooden rod (C) , and make a notch 
(0.2 cm deep) around the rod 
about 0.5 cm from the end. 
Place the spring device in the 
appropriate slot in the cart, 
and anchor it in position by 
means of the screw (F) inserted 
through the top plate of the 
cart in such a way as to pass 
through the loop on the end of 
the spring. 



-77- 



(3) Spring Release System 



Wooden 
Rod (C) 



Wood (J) 




Top (B) 



Rubber 
Stopper (E) 



Metal 
Strip (G) 

Cross Section 



Body (A) 



Top (B) 



Bolt (H) 



Nuts (I) 




Wood (J) 



Metal 
Strip (G 



Spring Slot 



(4) Wheel System 



Bend the sheet of aluminum (G) 
into an "L" shape (8 cm wide, 
2 cm tall, with a base of 1cm) . 
Attach the sheet to the front of 
the cart so that the base of the 
sheet just overlaps the slot for 
the spring device. In this way 
the spring may be compressed and 
held in position by means of the 
metal sheet and the notch in the 
rod. 

Use the bolt (H) and two appro- 
priate nuts (I) to serve as a 

releasing device, and bore a 
hole through the metal sheet and 
top plate of the cart, 1 cm from 
the front, so as to expose the 
rod of the spring device. 

The diameter of the hole should 
be large enough to admit the 
head of the selected bolt. 

Drill a hole through the middle 
of the wood strip (J). The 
diameter of the hole should be 
just large enough to admit the 
bolt (H) , but not the head of 
the bolt. Place the bolt through 
the strip with the bolt head 
beneath the strip, such that it 
sits in the newly drilled hole 
in the body of the cart. Nail 
the strip in position on the 
front of the cart, and add the 
two locking nuts (I) to the end 
of the bolt. 

Three ball bearing wheels (K) 
will have to be purchased 
(possibly imported) for this 





Nail (M) 



I -Axle 



Front 
Wheel (K) 



Rear 
Wheel (K) 



Axle 



'— Nail 



Top View 



cart. Cut two axles from the 
wooden dowel (L) . Make the 
front axle 13 cm, and rear 9 cm 
long (both 0.5 cm in diameter in 
this instance) . The diameter of 
the dowel should be the same as 
the internal diameter of the 
ball bearing wheels, thus pro- 
viding a tight fit. 

Pass the axles through the axle 
holes in the cart and fit the 
wheels appropriately on the 
axles. Take the four small 
nails (M) , and drill holes of 
the same diameter as the nails 
through the axle ends. Insert 
the nails through the holes, 
thus securing the axles and 
wheels in position. 



(5) Bumpers 



Bumpers 





— 1 1 


1 




1 1 




~-5.5-H 

f3h 






|—5.5 — ' 




■-V y 









• 


-o- 




^^S— 






^^ 




Side 


View 





Use the two strips of wood (N) 
as bumpers. Nail them in posi- 
tion on top of the cart in such 
a way that they will hold a 
second cart (placed on top of 
the first) firmly in position. 



-79- 



c . Notes 

(i) The final weight of the cart will be of the order of 1,000 g. With ball 
bearing wheels this will not produce too much friction, while it will result in 
the moving cart having high momentum, and the cart will be little affected by what 
friction does exist. 

(ii) A whole range of experiments related to force and motion will be found in 
many laboratory books, for example The Physical Science Study Committee, Labora- 
tory Guide , (USA: D. C. Heath and Company, 1965) . 



IV. WAVE MOTION APPARATUS 

A. RIPPLE TANK APPARATUS 

There are many ways of introducing wave motion to students, through observations 
of waves in water, heat radiation, acoustics, optics and electromagnetism. Each 
approach requires a different set of equipment. The materials here are limited to. 
presenting wave motion through the observation of waves on water, and the equipment is 
thus limited to ripple tanks and accessories. 



A. RIPPLE TANK APPARATUS 



Al. Ripple Tank 



© 



(7) Vibrator Unit 



(1) Basic Tank 




(6) Lamp Support 



5) Lamp Housing 



(4) Legs 



3) Outlet 



a. Materials Required 
Components 
(1) Basic Tank 



Qu Items Required 

2 Woo d (A) 

2 Woo d (B) 

1 Glass Plate (C) 

1 Rubber Based Cement (D) 



Dimensions 

60 cm x 3 . 5 cm x 3 . 5 cm 
57 cm x 3 . 5 cm x 3 . 5 cm 
57 cm x 57 cm x . 3 cm 



©From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide , (London: Centeir fo Educational Development Overseas iy/z) , pp s^-yi. 



-B2- 



(2) Beach 



(3) Outlet 



(4) Legs 



(5) Lamp Housing 



(6) Lamp Support 



(7) Vibrator Unit 



4 Soft Wood (E) 

4 Brass Discs (F) 

1 Metal Tube (G) 

1 Rubber Stopper (H) 

4 Wood (I) 

4 Bolts (J) 

4 Wing Nuts (K) 

1 Aluminum Sheet (L) 

1 Plywood (M) 

1 Aluminum Sheet (N) 

1 Lamp (0) 

1 Electrical Socket (P) 



: 


Wood (Q) 




i 


Bolt (R) 




1 


Wing Nut (S) 




1 


Wood (T) 




1 


Triangular Wood 


(U) 



1 Packing Case Steel Band (V) 

2 Aluminum Strips (W) 

2 Packing Case Steel Bands (X) 

2 Glass Marbles (Y) 

2 Wood (Z) 

1 Bolt (AA) 

1 Wing Nut (BB) 



56.5 cm x 6 cm x 2 cm 

0.05 cm thick; 3 cm 
diameter 

5 cm long, 1 cm diameter 

2 . 5 cm diameter, 2 . 5 cm 
deep 

60 cm x 3 cm x 2 cm 

3 cm long, . 4 cm 
diameter 

. 4 cm internal diameter 

35 cmx 16 cmx 0.05 cm 

11 cm diameter, . 4 cm 

thick 

15 cm diameter, 0.05 cm 
thick 

100 watt, straight 
filament 

Fits above lamp 

65cmx3cmx2cm 

4 . 5 cm long, . 3 cm 
diameter 

. 3 cm internal diameter 

4 8cmx2cmxlcm 

5 cmx 4 cm x 3 cm, and 

1 cm thick 

7 cm x 0.5 cm x 0.02 cm 

1.5 cm x 0.6 cm 
x 0.02 cm 

30 cm x 1 cm x 0.05 cm 

1.5 cm diameter 

7 cm x 2 cm 2 1 cm 

2 . 5 cm long, . 4 cm 
diameter 

. 4 cm internal diameter 



b. Construction 
(1) Basic Tank 



Out of each of the side wood 
strips (A and B) cut a single 
length approximately 2.0 cmx 
2.0 cm, (A small circular 




Section of Upper 
.Frame (A/B) 



Section of 

Lower Frame (A/B) 




Joint in Lower Frame (A/B) 





Lower Frame (A/B) 



Upper Frame 



Cement 




♦-Glass Plate (C) 



Cement 



Lower Frame 

Cross Section of Frame 



Temporary Nail 




Glass Plate 



saw is useful in performing 
this task) . You now have four 
large pieces of wood to make 
the lower frame, and four small 
pieces to make the upper frame. 



The end pieces of the shorter 
lengths for the lower frame are 
cut (as illustrated) so that 
they may be firmly joined 
together with wood cement. 

Set the glass plate (C) on the 
ledge of the lower frame. 
Cover the edges of the glass, 
and the inner edges of the 
lower and upper frame with a 
waterproof cement (D) as 
illustrated. An asphalt or 
rubber based cement is ideal . 
Set the glass on the ledge of 
the lower frame, and hold it 
in position by placing the 
upper frame on top of ±t . 



The whole frame may be held 
together by clamps, or nails, 
tacked temporarily through 
the two frames, until the 
cement is dry. 



Frame 



Cross Section of Frame 



You now have a basic tank with 
an inner and outer frame 
insuring the tank is leak proof. 



(2) Beach 




The beach is any device which 
will cut out unwanted reflection 
from the sides of the tank. 
One of the most effective, and 
durable of beaches is made 
from soft pine wood (packing 
case material) . Make the beach 
rather like a picture frame 
from the softwood (E) so that 
it sits on the glass surface 
of the tank, and fits snugly 
within the upper frame. 



Tank Frame Beach (t) 



Plan of Frame and Beach 




The most important aspect of 
the beach is the angle of the 
surface as it slopes downward 
from its outer to inner edge. 
The dimensions of a cross 
section to cope with water 
depths varying from 0.5 cm to 
1.5 cm is illustrated. 

Smooth the surface of the beach 
with fine sandpaper (leaving a 
smooth, but porous, surface) , 
but do not varnish. Wetting 
the surface of the beach at 
the commencement of a series 
of experiments makes the 
damping of the waves most 
effective. 



(4) Legs 



Hole 




Wing Nut (K) 



Slot 



Bolt (J) I" set 



Top of Leg U) 



(5) Lamp Housing 



may be assisted by tilting the 
tank towards the corner. The 
bottom edge of the outlet hole 
should be at the same level as 
the top surface of the glass 
(or just a little below) , 

Seal the metal tube (G) into 
the horizontal hole with a 
waterproof cement. Bore a hole 
(0.9 cm diameter) partway into 
the rubber stopper (H) using an 
electric drill (not a cork 
borer) . Fit the stopper on the 
tube, thus controlling the 
outflow of water. 

Drill and chisel a slot (2 cm x 
0.5 cm) in the top of each of 
the four wood pieces (I) to make 
adjustment slots for the legs. 
Make four insets (0.3 cm deep) 
in the frame to hold the legs 
firmly in a vertical position. 
Then, drill a horizontal hole 
(0.4 cm diameter) through the 
lower part of the outer frame 
(that is beneath the level of 
the glass) at the middle of 
each inset. Attach each leg 
to the frame with a bolt (J) 
passed through the hole in the 
frame and the slot in the leg. 
Fasten the bolt and leg firmly 
in position with a wing nut (K) . 

The size of the lamp housing 
will be dependent on the size 
of the contained lamp. In 
this case the lamp (0) utilized 
was 8 cm from the socket to 



-87- 



0.8T [ 




*$\ Endpiece 



Sheet (L) 



Aperture 



Endpiece 



II O.E 



Filament 
Lamp (0) 



to filament. Ideally the fila- 
ment should be a straight line, 
but a slightly bent filament 
such as that illustrated will 
serve the same purpose. 

To make the housing for the 
above lamp take a sheet of 
aluminum (L) and cut an aperture 
(5 cm x 5 cm) from its center. 
Roll the sheet into a cylindrical 
shape, and hold it in position, 
by means of bent end pieces. 



U 8 



11 




Housing 




Lid (N) 



Lamp (0) 



Socket (P) 





Lid (N) 



Hole 



Socket 

Hole Endpiece (M) 



Filament 
Position 



Attach the hardboard or plywood 
endpiece (M) to the base of the 
container with very small nails. 
Drill a central hole in the 
endpiece to facilitate the 
placement of the lamp (0) and 
electrical socket (P) . Complete 
the housing by making a lid out 
of aluminum sheet (N) . Drill 
a small hole (0.2 cm diameter) 
in the lid, such that it is in 
line with the filament. 



-88- 



(6) Lamp Support 



Bolt (R) 




Slot 
r ..(2»_Wing Nut (S) 

Lamp Support (Q) 



Tank Frame (A/B) 




Horizontal 

Component (T) 



Slot 



Vertical 
Component (Q) 



The vertical component of the 
lamp support is made, and at- 
tached to the ripple tank, in 
very much the same way as the 
legs. Drill and chisel a slot 
(7 cm x 0.5 cm) near to the 
bottom of end wood (Q) to 
permit adjustment. Attach the 
support to the ripple tank 
frame with bolt (R) passed 
through the lower part of the 
frame, and held in position by 
wing nut (S) . 

Cut a rectangular slot (2 cm x 
1 cm) in the top of wood (Q) 
to take the horizontal component, 
wood (T) . Fasten the two 
firmly together with wood 
cement. Glue a triangular 
piece of wood (U) between the 
two components to make a 
stronger junction. 



1 




Wood (U) 



y^ 



tr^ 



2.0 



0.5 s '- — * 



Strip (V) 
Folded 




Strip (W) 



•Strip (V) 



l -tSi 



In order to attach the lamp 
housing to the horizontal 
components of the support make 
two brackets from steel strips 
(V) as illustrated. Cut four 
horizontal slots in the upper 
part of the lamp housing and 



-89- 



Bracket (V) 



Support (T)- 



^33 



Slot 




S=v^\ 



Lamp Housing 



pass the steel strips through. 
Fasten the loose ends of the 
brackets together with folded 
pieces of aluminum (W) . Then 
slide the brackets over the 
lamp support . 



(7) Vibrator Unit 



Steel Strip (X) 



JO 



Sphere 




Bolt (AA) 



c. Notes 



The steel strips (X), or stiff 
coat hanger wire, will serve 
as the arms of the vibrator. 
Attach a glass sphere (Y) to 
the end of each arm using epoxy 
resin. 

Make the vibrator clamp from 
two strips of wood (Z) . Drill 
a hole (0.4 cm diameter) through 
the lower strip, and then attach 
the strip to the frame with two 
screws. Set the top strip on 
top of the first, and fasten it 
in position with the bolt (AA) 
and wing nut (BB) . The vibrator 
arms may now be clamped firmly 
between the strips of the clamp, 
being held at the middle of the 
arms. This insures the maximum 
possible period of vibration. 



(i) With the help of the Ripple Tank Accessories (IV/AZ) it is possible to 
observe the phenomena of reflection, refraction, interference and diffraction in 
waves created in the Ripple Tank. 



-9o- 



AZ . Ripple Tank Accessories 



© 



(1) Depth Marker 




U) Straight Line Source 



(3) Straight Barriers 



Curved Barrier 




(5) Rectangular Glass Plate 



(6) Curved Glass Plate 



S~*~fc — (7) Vibrator Mass 



a. Materials Required 



Components Ou 


Items Required 


(1) Depth Marker 1 


Coat Hanger Wire 


(2) Straight Line 1 


Wooden Dowel (B) 


Source 




2 


Nails (C) 


(3) Straight Barriers 1 


Wood (D) 


: 


Wood (E) 


2 


Wood (F) 


1 


Wood (G) 


(4) Curved Barrier 1 


Hose Pipe with 




Smooth Surface (H 



Dimensions 
10 cm long 

40 cm long, 2 cm 
diameter 

15 cm long approximately 

4 cm x 2.5 cm x 1 cm 
15 cm x 2.5 cm x 1 cm 
10 cm x 2.5 cm x 1 cm 

5 cm x 2.5 cm x 1 cm 

55 cm long, 2 cm 
diameter 



(5) Rectangular 
Plate 

(6) Curved Glass 
Plate 



Glass Sheets (I) 



Glass Sheets (J) 



25 cm x 15 cm x 0.4 cm 



25 cm x 15 cm x 0.4 cm 



©From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 

Guide, (London: Center for Educational l Development Overseas, 19/2) \ pp 92-95. 



-91- 



(7) Vibrator Mass 



b. Construction 



;i) Depth Marker 



1 Iron Bar (K) 
1 Bolt (L) 



Marker (A) 



(2) Straight Line Source 




Nail (C) 



(3) Straight Barriers 





Lead Cover 



Lead Cover 
(4) Curved Barrier 



11 cm x 2 cm x 0.3 cm 

0.2 cm diameter, 
1 cm long 



Mark off the end of wire (A) 
in half centimeter intervals 
(0-2 cm) . The marker may then 
be used to determine the depth 
of the water at the four 
corners of the ripple tank, 
and makes the levelling of the 
tank simpler. 

Bore holes into both ends of 
the wooden dowel (B) and insert 
long nails (C) into the holes 
to prevent the rod from floating 
in the ripple tank. 



Nail thin strips of lead along 
the sides and base of the pieces 
of wood (D, E, F and G) to 
prevent them from floating in 
the ripple tank. The weighted 
pieces serve as suitable 
barriers . 

A smooth surfaced hose pipe (H) 
serves as a suitable curved 
barrier. The pipe may be curved 
into any desired arc. 



(5) Rectangular Plate 



Take a sheet of glass (0.4 cm 
thick) and mark out two sections 
(each 25 cm x 15 cm x 0.4 cm) 
with a glass cutter. Break 
the glass along the marks by 
hand, The two newly produced 
sheets (I) may be set one on 
top of the other in water, thus 



-92- 



Curved Glass Plate 




(7) Vibrator Mass 



Bolt (L) 




Bar (K) 



Vibrator Arm 



creating a plate of thickness 
0.8 cm. 

Scratch guidelines on the glass 
plates (J) in the shape of a 
parallelogram. Cut along the 
lines with a glass cutter, and 
break the glass along the lines. 
Grind down the shape to a 
curve, as indicated, with the 

help of a sandstone. The two 
plates may be used one on top 
of the other in the ripple tank, 
making a plate of thickness 
0.8 cm. 

The soft iron bar (K) should 
weigh approximately 50 g. 
Place the bar in a strong 
clamp, and use a hammer to bend 
it in half so that it becomes 
two parallel bars about 0.3 cm 
apart. Drill a hole (0.2 cm 
diameter) in the middle of the 
top bar, and make a thread 
(0.2 cm diameter) in the hole. 
Screw bolt (L) into the hole 
thus making it possible to 
clamp the bar onto the ripple 
tank's vibrator arm. 



-93- 



A3. Stroboscope 



© 



(1) Wheel 




(2) Handle 



a. Materials Required 
Components 

(1) Wheel 

(2) Handle 

(3) Pivot 



Qu Items Required 
1 Hardboard (A) 

1 Wooden Dowel (B) 



! 



Bolt (C) 



1 Wing Nut (D) 

1 Nut (E) 
1 Wood (F) 



Dimensions 

25 cm diameter, 
. 3 cm thick 

25 cm long, 

2 cm diameter 

4.5 cm long, 
0.4 cm diameter 

0.4 cm internal 
diameter 

0.4 cm internal 
diameter 

3 cm diameter, 
1.5 cm thick 



© From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 



Guide, (London: Center for Educational Development Overseas, 19/2) 



PP 



)/. 



-94- 



(1) Wheel 



0.3- 




Finger 
Hole 



Cut the stroboscope wheel from 
the piece of hardboard (A) . 
Make. 12 equally spaced slits 
in the perimeter of the wheel. 
Drill a finger hole (2 cm 
diameter) at a distance of 3 cm 
from the center of the wheel, 
and a pivot hole (0.5 cm 
diameter) at the center of the 
wheel . 



(2) Handle 



(3) Pivot 



Wing Nut (D) 



Handle 




Spacer (F) 



The handle is simply a wooden 
dowel (B) . Drill a hole 
(0.4 cm diameter) through one 
end of the handle to take the 
pivot bolt (C) . 

Use the bolt (C) to serve as 
the pivot for the wheel. Insert 
this through the wheel, the 
spacer (F) , a locking nut (E) 
and the handle (B) . Use the 
locking nut (E) and the wing 
nut (D) to hold the handle in 
a fixed position on the pivot, 



Bolt (C) wh eel 



c. Notes 



Detail 
(Cross-section) 



(i) If the components of a moving body repeatedly take up fixed positions at 
regular intervals (e.g., vibrating bodies, waves) it is possible to "stop" the 
motion by viewing it through the slits of the stroboscope, rotated at an 
appropriate speed. 



V. THE MULTIPURPOSE SYRINGE 

The purpose of this chapter is to illustrate some of the multiple uses to which a 
syringe may be applied. The syringe devices are therefore grouped according to the 
concepts they are intended to illustrate. 

A. AIR PRESSURE APPARATUS 



The devices in this section are all concerned with varying air pressure in the 
syringe. 

B. SPECIFIC GRAVITY APPARATUS 

The syringes in this section are used in one way or another to determine the 
specific gravity of solids and liquids. 



-ye>- 



A. AIR PRESSURE APPARATUS 



Al . Hydraulic Press 




(1 | Support 



(2) Syringe 
Assembly 



a. Materials Required 






Components 


QU 


Items Required 


(1) Support 


2 


Wood (A) 




2 


Wood ( B ) 



(2) Syringe Assembly 1 



Plastic Disposable 
Syringe (C) 

Plastic Disposable 
Syringe (D) 

Rubber Tube (E) 
Fine Wire (F) 



Dimensions 

20 cm x 5 cm x 2 cm 

17 cm x 5 cm x 2 cm 

10 cc capacity 

60 cc capacity 

20 cm long, . 5 cm 
diameter 

5 cm long 



3, Construction 
(1) Support 



Nail the two shorter pieces 
of wood (B) to the ends of 
one of the longer pieces (A) 
in upright positions. Before 



-97- 




cr> 



Holes 

A 



(B) 



\ 




/ 



\ 



(A) 



nailing the last piece (A) 
into position across the top 
of the support, two holes 
must be drilled in it. These 
holes must be slightly larger 
in diameter than the barrels 
of the syringes used. Make 
these holes about 10 cm apart. 



(2) Syringe Assembly 



Attach one end of the rubber 
tube (E) to the nozzle of 
the larger syringe (D) . Wrap 
one piece of wire (F) around 
this joint to seal it as 
tightly as possible. With- 
draw the plunger of this 
syringe halfway to fill it 
with water through the end 
of the rubber tube, Try to 
eliminate as many of the air 
bubbles from the syringe as 
possible, 

Holding the free end of the 
rubber tube so that no water 
can escape, run the end of 
the tubing through, the hole 
in the support and put-the 
large syringe into position. 
Put the barrel only of the 
small syringe (C) into posi- 
tion, and connect the end of 
the rubber tubing to the 



-98- 



nozzle. Again, use the wire 
(F) to make the junction 
tight. Push the plunger of 
the large syringe down until 
the water rises in the small 
syringe and is about to run 
over. Insert the plunger of 
the small syringe now and 
push down, and a minimum of a 
air should be trapped in the 
system. 



c. Notes 



(i) The lifting power of the hydraulic press may be felt by exerting a gentle 
downward pressure on each syringe simultaneously with both hands. The load on 
the smaller syringe will lift the plunger of the larger syringe, even when the 
load on the latter is felt to be greater than that on the smaller syringe. 



-99- 



AZ . Vacuum Apparatus 



(1) Fixed Syringes 




(2) Clamp and 
Tube 



a. Materials Required 
Components 
(1) Fixed Syringes 



(2) Clamp and Tube 



b, Construction 

(1) Fixed Syringes 



Qu I tems Required 

1 Plastic Disposable 
Syringe (A) 

1 PlasticDisposable 
Syringe (B) 

2 Nails ( C ) 

j Plastic Tube (D) 

Screw Clamp (E) 



Nail (C) 



Syringe (A) 



Q): 






T3) 




4- 



(o 



25 cc Volume 



Dimensions 

35 cc capacity 

10 cc capacity 

4 cm long 

20 cm long, 0.5 cm 
diameter 

CHEM/IV/A5 

Use a drill of a slightly 
larger diameter than that of the 
nails (C) to carefully make 
holes through the barrel and 
plunger of the plastic syringe 
(A) , When the nail (C) is 
inserted through these holes, 
the plunger should be held in 
a position such that the volume 
in the syringe is 25 cc. 
Similarly, prepare the second 
syringe (B) so that the volume 
is held at 5 cc capacity when 
the nail is in place. 



(2) Clamp and Tube 



Clamp 
Here 




Connect the two syringes with 
the length of plastic tube (D) . 
Be certain the connections 
between the nozzles and tubing 
are tight. Also, the tubing 
must be flexible enough to 
allow the clamp to close it off 
completely while, at the same 
time, it should be elastic 
enough not to collapse as 
pressure in the system becomes 
lower. The clamp (E) will close 
off air flow through the tube 
most easily when the tube is 
doubled over against itself. 



c. Notes 



(i) To use this piece of eguipment to create a vacuumin, the larger syringe (A) , 
first fix the volume of the air in the syringe (A)at 25 cc using the nail to hold 
the plunger in position. Connect the clamp and tubing to it. Depress the plunger 
in the smaller syringe (B) completely, then fasten the syringe to the tubing, and 
close the clamp. Now, open the clamp and withdraw the plunger in the smaller 
syringe. This will extract air from the larger syringe. Fix the plunger of the 
smaller syringe with the nail, and reclose the clamp. Remove the smaller syringe 
from the tubing. 

The extraction procedure may be repeated f 1 ve or six times in succession in 
order to produce very low pressures. 

(ii) After one or more extractions, the reduceopressure in the large syringe may 
be determined by holding the syringe under water and removing the clamp from the 
tube. Water will rise in the syringe until the trapped air is once again at 
atmospheric pressure. Note the volume of the trapped air. 

If 

The volume of air finally trapped above water = V2 
The pressure of air finally trapped above water = P2 
(Where ?2 = atmospheric pressure) 

And if 

The volume of same mass of air prior to contraction = V^ 
(Where Vj = volume of syringe) 
The pressure of same mass of air prior to contraction = Pi 



Then 



-101- 

The pressure of the vacuum created is given by 

P 9 V ? 

(iii) In a typ ical experiment (results i ndicated below) five extractions reduced 
the pressure in the large syringe to 0.5 atmosphere pressure. 



No.0 f 


v 2 


v l 


p l 


Extractions 


cc 


cc 


Atmospheres 


1 


25 


23 


0.92 


2 


25 


19.5 


0.78 


3 


25 


16.5 


0.66 


4 


25 


14.5 


0.58 


5 


25 


12.0 


0.48 


6 


25 


10.5 


0.42 



Pressure in 


Atmospheres 


, 


. 


1.0 




0.9 




0.8 


- 


0.7 


- 


0.6 





0.5 



0.4 



-S- Number of 

Extractions 



-102- 



A3 . Elasticity Device 




(] ] Syringe 



a, Materials Required 

Components 
(1) Syringe 

b. Construction 
(1) Syringe 



c, Notes 



Qu 



Items Required 

Plastic Disposable 
Syringe (A) 



Dimensions 

Size can be variable 



Place a finger over the air 
outlet to seal the air in 
the tube. 



(i) With a sealed syringe, elasticity of air may be felt by pushing down or 
pulling out the plunger. In either case, if the syringe is airtight, the plunger 
will be pushed or pulled back to its original position by the air trapped in the 
syringe : 

(ii) It is of interest to replace the air in the syringe by water in order to 
compare the elasticity of water with that of air, 



-103- 



A4 . Gas Expansion Device 



© 



Q 



CLX^- 



11) Syringe Unit 




a. Materials Required 
Components 
(1) Syringe Unit 



b. Construction 

(1) Syringe Unit 



Qu Items Required 

1 Plastic Disposable 
Syringe (A) 

2 Beakers (B) 



Dimensions 

Size can be variable 

Approximately 250 ml 

Any size syringe (A) may be 
used, but one approximately 
10 - 15 cc in capacity is 
convenient, Fill one beaker 
(B) with hot water and the 
other with cold water. 

c. Notes 

(i) After the syringe has been filled with suitable gas (e.g., air) it is 
placed in the cold water bath for several minutes. It is then removed, emptied 
of any water which may have entered through the open nozzle, adjusted to a volume 
of 5 or 10 cc, and placed in the hot water bath, As the gas expands, bubbles will 
leave the syringe. After the bubbling has ceased, remove the syringe and place 



SFrom Andrew Farmer, "The Disposable Syringe: Additional Experiments," S chool 
Science Review, CLXXVIII (1970), pp 59-60. 



-104- 



it back in the cold water bath. As the gas contracts, water will enter the syringe, 
and the amount of water entering serves as a measure of the expansion of the gas. 
Quantitative data on gas expansion can be obtained by using the same gas and syringe 
and varying the temperature of the hot water bath, or by using the same syringe and 
hot water bath and varying the gases. 



-105- 



B. SPECIFIC GRAVITY APPARATUS 



Bl. Volume Determinator 



Q 



^D 



(1) Syringe 




a. Materials Required 
Components 
(1) Syringe 



b. Construction 



(1) Syringe 



Qu I tems Required 

1 Plastic Disposable 



1 



Syringe (A) 
Beaker (B) 



Dimensions 

Size can be variable 

Approximately 250 ml 

Choose a plastic, disposable 
syringe (A) with a barrel 
capacity large enough to hold 
the object whose volume is to 
be measured, Fill the beaker 
(B) about one half full of 
water. 

c. Notes 

(i) Use this apparatus by placing the object whose volume is to be measured 
into the syringe. Replace the plunger and depress it until it almost touches 
the object in the bottom of the syringe. Hold the syringe so that the end of it 
is under water in the beaker. Draw enough water into the syringe to cover the 
object by withdrawing the syringe plunger. Find the difference between the 



-Un- 
original syringe reaolng and the final syr 'Inge reading. This indicates the volume 
of water drawn into the syringe. Note the apparent volume of water in the syringe 
(that is the volume of the object and the water combined) and subtract from this 
the volume of water known to have been drawn into the syringe. The resultant va 
indicates the volume of the object. 



-107- 



B2 . Specific Gravity Device 




1) Syringe 



a. Materials Required 
Components 
(1) Syringe 

b . Construction 



0) 



Syringe 



Notes . 



Qu Items Required 

1 Plastic Disposable 
Syringe (A) 



Dimensions 

35 cc capacity 



Use the syringe (A) with no 
modification except to remove 
the needle, as usual. 



(i) To determine the specific gravity of a liquid, simply draw up 25 cc of 
the liquid, and find the mass of the liquid plus syringe. Subtract the mass 
of the empty syringe from this total to find the mass of the liquid. Divide 
the mass of the liquid by 25 to obtain the specific gravity. 

(ii) If the liquid should leak from the syringe, simply seal the nozzle of 
the syringe with a nail. Remember to add the mass of the nail into the 
calculations. 



B3, Hydrometer 



^S 



, (1) Weighted Syringe 




a. Materials Required 

Components Qu 

(L) Weighted Syringe 1 

6-8 

b. Construction 

(1) Weighted Syringe 



Items Required 

Plastic Syringe Barrel (A) 

Metal Washers (B) 



Dimensions 

35 cc capacity 

Slightly less wide 
than the barrel 



Place enough washers (B) in 
the syringe barrel (A) to 
cause it to sink to the 25 cc 
mark when placed in water. 
Seal the nozzle by heating it 
until it melts shut. 



c. Notes 



(i) For use as a hydrometer, the syringe barrel must be calibrated. Use a 
graduated cylinder (CHEM/III/B2) to make the calibrations. Note the water volume 
in the cylinder before and after the syringe barrel is placed in it. The difference 
of these two values indicates the volume of water displaced by the syringe. By 
this means it is possible to indicate a displacement value for each reading on th 
syringe. The following table was created for the syringe under test. 



-109- 



Scale on 


Volume of 


Syringe 


Water Displacement 


cc 


cc 


20 


27.2 


21 


28.6 


22 


29.2 


23 


30.4 


24 


31.5 


25 


33.0 


26 


34.5 


27 


36.1 


28 


37.5 


29 


38.4 


30 


39.6 



Weigh the syringe (and its washers), and then place it in the liguid 
whose density is to be determined. 

' (ii) 
I f 

V = The volume of liquid observed to be displaced 
M - The mass of the syringe and washers 



Then 
M 

M /V 



The mass of liquid displaced 

The density of the liquid displacec 



VI. OPTICS APPARATUS 

The apparatus in this section has been grouped according to the concepts, and are 
identified as follows: 

A. GENERAL APPARATUS 



This apparatus is for use in studying all aspects of optics whether this might be 
reflection and refraction, or interference and diffraction. 

B. REFLECTION APPARATUS 

This apparatus is sufficient for a simple study of reflection. The electroplated 
mirrors are preferable to brass mirrors described, although the latter will be found 
adequate for most purposes. 

C. REFRACTION APPARATUS 

Apparatus for the study of refraction using plastic prisms. 
D . LENS APPARATUS 



Apparatus to enable a study of the properties of lenses. 

E. DIFFRACTION AND INTERFERENCE APPARATUS 

A study of the basic phenomena of interference and diffraction is possible with 
this apparatus, using simple slits, holes and thin films. 



A. GENERAL APPARATUS 



Al. Light Source @ 




(1) Lamp Housing 



(2) Base 



a. Materials Reguired 






Components 


2u 


Items Reguired 


(1) Lamp Housing 


i 


Ripple Tank, Li 
Housing (A) 


(2) Base 


i 


Plywood (B) 




2 


Wood Strips (C) 




2 


Wood Strips (D) 


b. Construction 







(1) Lamp Housing 



Dimensions 

IV/A1, Component (5) 

21 cm x 11 cm x . 5 cm 
16 cm x 2.5 cm x 1 cm 
11 cm x 2.5 cm x 1 cm 

This lamp housing (A) is pre- 
cisely the same as that designed 
for the ripple tank (IV/A1) . 
All that is added is a base. 



©From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 19/2) , p 98 . 



(2) Base 




Plywood (B) 



C. Notes 



Wood 
Strip (C) 




Wood 
Strip (D) 



Make the base from the piece of 
plywood (B) . Nail the two short 
pieces of wood (D) to the ends 
of the plywood (B) and nail the 
remaining wood strips (C) to the 
plywood, too. Make sure that 
they will hold the lamp housing 
firmly in position. Then nail 
it into position. 



(i) This light source may be used in conjunction with the Slit/Aperture 
Combination (VI/AZ) to investigate the behavior of rays of light transmitted from 
the source. The light source is designed for use with all the items included in 
this chapter, including the interference and diffraction apparatus. If the bulb 
used is bright (e.g., 100 watts) , there will be no need to black out the labora- 
tory. 



A2 . Slit/Aperture Combination 



o o o 



coo 




(2) Framework 



(1) Metal Sheet 



a. Materials Required 
Components 
(1) Metal Sheet 

(2) Framework 



Qu Items Required 

1 Aluminum Sheet (A) 

4 Wood Side Strips (6) 

2 Wood Side Strips (C) 
2 Wood Strips (D) 



Dimensions 

15 cm x 10 cm x 0.02 

cm 

I cm x 1 cm x . 5 cm 
15 cm x 2 cm x 0.5 cm 

II cm x 2 cm x . 5 cm 



b. Construction 



(1) Metal Sheet 





i 




e o o — 
o c o 
c o c — 


-1 




6 


r 


2.5 




' 




/ 




• 5 » 



Support 
Block 




Cut the slit (0.1 cm width) and 
apertures (0.1 cm diameter) in 
any suitable thin sheeting (A) 
(metal, bakelite, cardboard) so 
long as the slit and apertures 
have clean cut edges. If the 
material used is relatively 
rigid, a small wooden block 
will provide adequate support. 
If the material tends to flex 
under its own weight, a frame- 
work, such as that indicated 
below, will be required for 
support . 



(2) Framework 




Wood 
— Strips (B) 



Sheet 
Metal (A) 



Wood 
Strips (D) 



Nail or glue two wood strips (B) 
to a third strip (C), leaving 
about a 0.1 cm gap between 
them. Make an identical piece 
from the other two narrow strips 
(B) and the one remaining wide 
strip (C) . Slide the metal 
sheet into position between the 
two pieces. 



-115- 




\ Wood 
/Strip (C) 



Nail the top and bottom pieces 
(D) to the two upright pieces 
to complete the framework. The 
thickness of the bottom strip 
(D) should not be much more than 
0.5 cm, as there is a tendency 
for this strip to cut off a 
desirable portion of any light 
path. 



Notes 



(i) The decision as to whether to use aframe will probably be one of economics. 
Thick metal sheets are much more expensive than thin ones, but the cost of labor 
involved in making a framework for a thin sheet may in some instances offset the 
difference between the two. 

(ii) The slit is primarily intended for delineating light rays (from the Light 
Source, VI/A) which may be traced across a horizontal surface. 

(iii) If the metal sheet is placed on itsside the apertures will sit at an appro- 
priate height in front of the Light Source (VI/A1) , and may be used as objects for 
experiments with lenses. 



-116- 



B. REFLECTION APPARATUS 



Bl. Mirrors and Electroplating 



© 



(1) Mirror 




(2) Holder 



a. Materials Required 
Components 

(1) Mirror 

(2) Holder 



b. Construction 



(1) Mirror 



Brass 
Strip (A) 



Qu I tems Required 
2 Brass Sheet (A) 

2 Metal Strapping (B) 

2 Plastic Tape (C) 




Wooden 
Block 



Dimensions 

10 cm x 2.5 cm x 0.1 cm 

Approximately 6 cm x 
2 cm x 0.02 cm 

2 c m x 1 c m 



Cut the sheet of brass (A) on a 
metal guillotine (to be found in 
your nearest metalwork shop) . 
If the metal sheet is cut with 
bench sheers some distortion is 
almost certain to result, thus 
lowering the quality of the 
mirror. If the mirror is to be 
curved, bend it over a smooth, 
curved, wooden block until the 
mirror becomes the arc of a 
circle of radius 8.5 cm. 



© From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 1972), pp 101-103. 



(2) Holder 




Plastic 

Tape (C) 



Polish the metal strips first 
with coarse carborundum paper, 
and then with successively 
finer and finer grades, taking 
care at each polishing to 
remove the deeper marks of the 
previous polishing. 

Obtain a mirror finish by 
polishing the surface with a 
soft cloth and metal polish. 

Bend the piece of metal packing 
case band (B) into a triangular 
shape. Curve the endpieces and 
cover them with the plastic 
tape (C) to protect the mirror 
surface. 



Slot 




Plastic 
Tape 



Alternatively, cut a slot (0.2 
cm wide) in a wooden block 
(2 cm x 2 cm x 2 cm) . Line the 
slot with plastic tape to prevent 
the wood from scratching the 
surface of the mirror to be 
held. 



c. Notes 

(i) Brass mirrors must be cleaned with metal polish before each usage. This 
process may be eliminated if the metal surface Js electroplated. The procedure 
to be followed is described below: 

Procure a plastic, or glass, container about 15 cm deep and 10 cm in 
diameter, and fill it with a nickel solution (e.g., Gleamax and Levelbrite) . 

Wash the polished brass mirror in caustic soda (soap) to remove grease and 
rinse with clean water. Grip the brass mirror in a crocodile clip, attached to 
an electrical lead, and suspend the brass mirror in the nickel solution. The 



mirror may be held in position by wrapping the electrical lead (by which it is 
suspended) around a wooden dowel bridging the container. 

Suspend a nickel plate in a similar fashion from a second electrical lead. 
We now have an anode (nickel plate) , a cathode (brass mirror) and an electrolyte 
(nickel solution) . 

Connect the anode to the positive terminal and the cathode to the negative 
terminal of a 6 volt battery, and pass a current through the nickel solution for 
15 to 20 minutes. The quality of the final surface will depend primarily on the 
quality of the initial polished surface, prior to electroplating. 



Brass 
Cathode 




Nickel 
Anode 



Nickel 
Electrolyte 



(ii) Mirrors may also be made by a very simple chemical process . Prepare three 

solutions as follows: 

I. 40 ml H 2 11-10 g Na0H ln - 10 ° ml Concentrated 

„„- „ fructose solution 

60 ml Concentrated NH 4 0H 100 ml H 2 (Glucose or any 

10 g AgN0 3 aldehyde may be 

used, although the 
reaction may be 
slower) . 

Just before using, mix equal volumes of solutions I and II. Then add the 

fructose solution to the new mixture in the ratio of 1:4. Silver will deposit on 

any glass surface in contact with the solution. If a microscope slide is placed in 

the solution, it will be coated on two sides. The external appearance will be 

dullish. Remove one such coating with a cloth. The glass-silver interface will 

be seen as an excellent mirror. 



B2 , Optical Board and Accessories 



(2) Steel Pins 




(3) Steel Pins 
with Sleeves 



(4) Protractor 



(1) Optical 
Board 



a. Materials Required 
Components 

(1) Optical Board 

(2) Steel Pins 



(3) Steel Pins with 
Sleeves 



(4) Protractor 

b. Construction 

(1) Optical Board 



(2) Steel Pins 



Qu I tems Required 

1 Hardboard (A) 

2 Steel Rods (B) 



2 



Steel Rods (C) 



2 Pencils (D) 

1 Aluminum Sheet (E) 



Dimensions 

4 cm x 4 cm x . 5 cm 

7 cm long, 0.1 cm 
diameter 

7 cm long, 0.1 cm 
diameter 

6.5 cm long 

10 cm x 5 cm x 0.05 cm 



This is simply a piece of hard- 
board (A) into which pins can be 
readily stuck. Normally a 
plain sheet of paper will be 
placed on top of the hardboard 
to facilitate the recording of 
experimental observations. The 
Refraction Model Apparatus 
(VI/C3) is such a piece of 
hardboard. 

The steel rods (B and C) may be 
cut from cycle spokes or similar 
steel rods. Sharpen one end of 
each rod with the help of a file. 



(3) Steel Pins with Sleeves 



(4) Protractor 




Aluminum Sheet (E) 



Remove the pencil lead from the 
pencils (D) with the help of a 
steel pin. Coat the steel pin 
(C) with epoxy resin, and slide 
it into the space originally 
occupied by the lead, so that, 
instead of the pencil lead, a 
steel pin protrudes from the 
end. Cover the sleeve with a 
white coat of paint. 

Make a protractor by cutting a 
semicircular piece of metal from 
the aluminum sheet (E) . Mark 
as many angles around the peri- 
phery of the protractor as 
desired. 



C. REFRACTION APPARATUS 



CI. Optical Prisms and Lenses 



© 





a. Materials Required 

Components 
(1) Prisms 

b. Construction 
(1) Prisms 



Inner 
Markings 



(1) Prisms 



Qu I tems Required 

1 Sheet of Acrylic (A) 



Dimensions 




Cutting 
Line 



16 cm x 10 cm x 2 cm 

Take the sheet of acrylic' (A) 
and mark out the shape of the 
desired prism with a sharp 
point. Draw a parallel set of 
lines about 0.5 cm outside the 
initial markinq. The inner 
markinqs should outline a tri- 
anqle (3 cm x 3 cm x 3 cm) , a 
rectanqle (8 cm x 5 cm) and a 
semicircle (9 cm diameter). 



Trianqular Prism 



(S) From Reginald F. Melton, E lementary, Economic Experiments in Physics, Apparatus 
Guide, (London: . Center for Educational Development Overseas, 1972), pp 106-108. 



-122- 



I I 


1 t ' 


' Markings | 


r o " 


( ' J 



Rectangular Prism 



_L 




Cutting 

Line 



Using a fine-toothed saw, care- 
fully cut the plastic down to 
the outer markings. The cut 
produced will have very jagged 
edges, the plastic showing a 
tendency to chip. This is 
normal, and should cause no 
concern. 



Semicircular Prism 




Glass 
Plate 



Carborundum 
Paper 



The next step is to remove the 
rough edges from the prism, 
reducing its size to that of 
the inner markings. For this 
purpose place a coarse sheet of 
Carborundum paper on top of a 
smooth surface (e.g., a strong 
glass sheet) . Then smooth down 
the surfaces of the prism by 
rubbing them on the Carborundum 
surface . 

Repeat the process with succes- 
sively finer and finer grades 
of Carborundum paper, taking 
care at each rubbing to remove 
the deeper marks of the previous 
rubbing. 



-123- 



Finally, replace the Carborundum 
paper by a sheet of plain paper. 
Drop a little metal polish on 
the paper, and repeat the 
rubbing process. The surface 
produced will be highly polished. 

The rubbing and polishing pro- 
cess is repeated with all the 
surfaces except that surface 
which will normally be in con- 
tact with the table top during 
experimentation. This surface 
is smoothed with Carborundum 
paper, but not metal polish, 
thus leaving the surface suffi- 
ciently rough to scatter light. 



c. Notes 



(i) Plastic is not as hard as glass, and is therefore more easily scratched 
and damaged. From time to time it is therefore necessary to repolish the surfaces 
with metal polish, as described above. 



-124- 



C2. Screen with Holder 



(1) Screen 




2) Hoider 



a. Materials Required 
Components 
(1) Screen 



(2) Holder 



b. Construction 



(1) Screen 



Qu I tems Required 
Cardboard (A) 
White Paper (B) 
Black Paper (C) 

Wood Block (D) 
Steel Band (E) 



Dimensions 

2 5 cm x 15 cm 

2 5 cm x 15 cm 

2 5 cm x 15 cm 

4 cm x 4 cm x 4 cm 

Approximately 

8 cm x 1 cm x 0. 02 cm 



Make the screen from the stiff 
piece of cardboard (A) . It is 
very convenient to have a front 
white surface and a rear black 
surface. This may be achieved 
by sticking appropriate sheets 
of paper (B,C) on the two 
surfaces . 



-125- 



(2) Holder 



Wood (D 




Strapping (E) 



Bend a length of packing case 
steel (E) as shown and nail i t 
to the side of the wooden 
block (D) . 



c. Notes 

(i) The white surface of the screen isused for normal image formation, while 
the black surface is useful whenever the screen is used as a barrier to exclude 
light. 



C3 . Refraction Model Apparatus 



( 3 ) Ramp 



(4) Ball Bearing 




(2) Supprts 



;i) Platform 



a. Materials Required 
Components 
(1) Platform 



(2) Supports 

(3) Ramps 

(4) Ball Bearing 

b. Construction 
(1) Platform 



Qu It ems Required 

1 Hardboard (A) 

2 Hinges (B) 

2 Wood (C) 

1 Wood (D) 

1 Wood (E) 

1 Ball Bearing (F) 



h7H 




Dimensions 

4 cm x 4 cm x 0.5 cm 

Approximately 2 cm 
long, sidepieces no 
more than . 5 cm wide 

30 cm x 4 cm x 2 cm 

12 cm x 5 cm x 2 cm 
12 cm x 3 cm x 2 cm 

2.5 cm diameter 



Cut a 7 cm strip from one side 
of the plywood (A) , and shape 
the newly cut edges back at an 
angle of 45° as illustrated. 
Reattach the 7 cm strip to the 
platform with very small hinges 
(B) avoiding the creation of a 
gap between the strip and main 
platform. Shape the free edge 
of the 7 cm strip to an angle 
of 45°. This shaping insures 
good contact between the strip 
and the table. 

(Also see illustration on next 
page. ) 



Hardboard (A) 



-rr 



Side View 




^L 



Hinge (B) 




Detail 



(2) Supports 



( 3 ) Ramp 




Books, or blocks of wood (C) , 
may be used to elevate the 
platform to different heights 
above the table top (e.g., 2 and 
4 cm) . 

Cut two triangular shapes out 
of the pieces of wood (D,E) . 
The height (h) of one triangular 
shape will be 5 cm and the 
other will be 3 cm, while both 
will have a base 12 cm long. 

The groove is best cut with the 
help of a saw. 



c. Notes 

(i) This apparatus is used to demonstrate the refraction of light according to 
Newton's Corpuscular Theory. The ball bearing may be rolled down the small ramp, 
across the top platform and down the ramp, °r alternatively down the large ramp, 
across the table top and up the ramp. In either case refraction occurs in crossing 
the ramp from one level (or medium) to another, and appropriate comparisons may be 
made with the transmission of light across a boundary (ramp) from one medium (level) 
to another. 



C4. Filter 




1) Cellophane 



(2)F 



rame 



a. Materials Required 
Components 

(1) Cellophane 

(2) Frame 

b. Construction 
(1) Cellophane 



Qu I tems Required 

1 Red Cellophane (A) 

2 Cardboard (B) 




Dimensions 
10 cm x 3 cm 

10 cm x 3 cm 

Test different strips of red 
cellophane (A) for suitability 
by noting what parts of a 
spectrum can be seen through the 
cellophane. The cellophane 
cutting out almost all colors 
other than red will be most 
suitable. 



(2) Frame 



0.5 




Cut the two pieces of cardboard 
(B) to the shape indicated, and 
stick (or clip) a suitable piece 
of red cellophane (A) between 
the two pieces. 



-129- 



c. Notes 

(i) Filters are very useful not only in studying the way in which different 
colors of light superimpose one on the other, but also for the creation of mono- 
chromatic light. This is particularly important in studying interference and 
diffraction phenomena. 



Dl. Lens with Holder 



© 



(2) Upri ght 



-130- 



LENS APPARATUS 




(3) Top Plate 



(4) Le 



(1) Base 



a. Materials Required 
Components 

(1) Base 

(2) Uprights 

(3) Top Plate 



(4) Lens 



Hn 


Items Required 


1 


Wood (A) 


2 


Wood Strips (B) 


2 


Screws (C) 



1 Metal Sheet (D) 

2 Screws (E) 

1 Magnifying Glass (f) 



Dimensions 

10 cmx5 cmxl cm 

12cmx2cmxlcm 
1.5 cm long 

7 cm x 1 cm x 0.1 cm 

Approximately 
0.7 cm long 



© From Reginald F. Melton, Elementary. Economic Experiments in Physic.?. Apparatus 
Guide, (London: Center for Educational Development Overseas, 1972), pp 120-121. 



b. Construction 



(1) Base 




Wood (A) 



Make two insets (0.5 cm deep) 
in the wood (A) to take the two 
uprights (B) . Drill a small 
hole (0.2 cm diameter) in the 
middle of each inset. 



(2) Uprights 



(3) Top Plate 



Lens 



Set the uprights (B) in the 
base insets with wood cement, 
insuring a firm joint by 
screwing the very small screws 
(C) through the base into the 
upright . 

Cut the top plate out of 
aluminum or brass (D) . Drill a 
small hole (0.2 cm diameter) at 
a distance of 1 cm from each 
end. Attach the top plate to 
the uprights with very small 
screws (E) . 

Purchase a suitable magnifying 
glass (F) locally. It may be 
held in any position on the 
upright by means of rubber bands. 



D2. Multiple Slits 




;i) Framework 



(2) Nails 



a. Materials Required 
Components 

(1) Framework 

(2) Nails 

b. Construction 
(1) Framework 



q u Items Required 
2 Wood Strips (A) 
2 Wood Strips (B) 



1 



Box of Nails (C) 




Indentatj 



Dimensions 

10 cm x 2 cm x 0.5 cm 

4cmx2cmxo . 5cm 

0.2 cm diameter, more 
than 4 cm long 



Make regular indentations down 
the middle of the top and 
bottom strips (A) of the frame- 
work, the indentations being 
0.4 cm apart. These indenta- 
tions can easily be made with 
a hammer and nail. The remain- 
ing two pieces of wood (B) will 
serve as sidepieces for the 
framework. Do not complete 
construction of the framework 
until the nails (C) are in place. 



-133- 



(2) Nails 



, Cut Here 



/ 



Take a handful of nails (C) and 
cut off the top ends to produce 
a uniform set of nails, each 
4 cm long. Tap the nails into 
the bottom strip (A) , position- 
ing them in the indentations. 
Then press the upper strip (A) 
onto the upright nails, using 
the indentations on the upper 
strip for guidance in position- 
ing the nails parallel to one 
another. Finally, attach the 
sidepieces (B) of the framework 
using very small nails or wood 
cement . 



c . Notes 

(i) The multiple slits are used primarily to break up beams of light into 
multiple pencils of light. Many alternative devices could be used for the same 
purpose, e.g., a hair comb supported by a wooden block. 



E . DIFFRACTION AND INTERFERENCE APPARATUS 



El. Fixed Single and Double Slits 




1) Fixed Slits 



a. Materials Required 
Components 

(1) Fixed Slits 

b. Construction 

(1) Fixed Slits 



Qu I tems Required 
1 Exposed Film (A) 




Exposed Film (A) 



Dimensions 

Approximately 
5 cm x 3.5 cm 



Take an exposed strip of film 
(A) (or a slide coated with 
colloidal graphite) and draw a 
straight line across it using 
a razor and a straight edge as 
a marker. The width of the 
slit may be increased, if 
desired, by drawing the razor 
over the same approximate line 
two or three times. Do not cut 
through the film. 

A double slit may be made in an 
almost identical way, Simply 
hold two razors face to face, 
and draw the lline across the 
film with the two razor blades 
pressed closejly together. The 
space between the slits may be 
increased, if desired, by hold- 
ing the blades at an angle to 
the vertical as the double line 
is drawn against the straight 
edge. 



-135- 



c . Notes 

(i) In making single or double slits it is well worthwhile repeating the pro- 
cedure several times on different parts of the film, and then selecting the best 
slits after testing, i 

(ii) Ifthe slits are held in a vertical position close to the eye, and if the 
vertical filament of the Light Source (VI/A1) at a distance of about three meters 
is viewed through the slits, interference and diffraction patterns will be 
observed even in daylight. The patterns are clarified by the use of the Filter 
(VI/C4) placed in front of the slits. 



E2, Adjustable Single Slit 




(1) Adjustable Slit 



a. Materials Required 
Components 

(i) Adjustable 
Slit 

b. Construction 

(1) Adjustable Slit 



Qu 
2 



I terns Required 
Razor Blades (A) 
Metal Strip (B) 



Dimensions 



Approximately 
7 c m x 2 c m 



Hold the two razor blades (A) 
against the metal strip (B) so 
that the edges of the blades 
are almost touching and are 
parallel to one another. 

c. Notes 

(i) If the slit is held in a vertical position close to the eye, and the 
vertical filament of the Light Source (VI/A1) viewed at a distance of about 
three meters, a diffraction pattern may be observed in daylight conditions. The 
pattern is clarified by the use of the Filter (VI/C4) placed in front of the slit. 
The effect on the pattern of changing the slit width may readily be observed. 



E3. Diffraction Holes 




(1 ) Metal Strip 



lyhterials Required 
Components 
(1) Metal Strip 



b. Construction 

(1) Metal Strip 



Qu I tems Required 
1 Metal Strip (A) 



Dimensions 

10 cm x 2.5 cm x 
0.1 cm 



Drill four holes (diameters 
approximately 0.1, 0.08, 0.05, 
and 0.02 cm) in the metal strip 
(A) at regular intervals. 



c . Notes 

(i) Circular diffraction patterns may be studied with these holes and the 
Light Source (VI/A1) placed in such a position that the light filament is viewed 
through the small hole in the lid of the lamp housing, thus acting as a point 
source. If this point source is viewed at a distance of about three meters by 
looking through one of the diffraction holes, when the strip is held close to 
the eye, a diffraction pattern will be seen even in daylight conditions. The 
pattern will appear clearer if the Filter (VI/C4) is placed in front of the 
diffraction hole. 



E4. Interference Strips 



(2) Handle 




' (1) Metal Strip 



a. Materials Required 

Components 

(1) Metal Strip 

(2) Handle 

b. Construction 

(1) Metal Strip 



(2) Handle 



Qu I tems Required 

1 Metal Strip 

(Copper or Steel) 



1 



Wood 




Slit 



Dimensions 

14 cm x 1 cm x 0.1 cm 

7 cm x 1 cm x 1 cm 

The metal strip (A) may be of 
any desired metal. In this 
instance, two are specifically 
recommended, namely copper and 
steel (from packing case bands) 

The handle is made from the 
wood (B) . Cut a slit down the 
middle of the handle with a 
saw. Cement the metal strip 
into this inset with epoxy 



c. Notes 

(i) If the end of the metal strip is placed in 'a hot flame, interference bands 
will be produced on the strip. 



VII. LABORATORY ACCESSORIES 

Where a science room has an electric outlet teachers will wish to take advantage 
of the mains' supply. The apparatus described here considerablyextends the usefulness 
of the electric outlet. 

A. TRANSFORMERS 



This section describes different types of transformers which may be used to produce 
low voltage AC outputs. The limitations of each transformer are carefully described 
in the notes. 

B. RECTIFIERS 

This section describes rectifiers, which may be used with the foregoing trans- 
formers, to produce low voltage DC current. 



A. TRANSFORMERS 



Al . Transformer, Iron Wire Core (6 volt output, 120 volt mains ) 



(1) Coils (Not visible) 




3) Base 



a. Materials Required 
Components 
(1) Coils 



(2) core 



(3) Base 



q u Items Required 

1 Sheet of Cardboard (A) 

1 Roll of Magnet Wire (B) 

1 Roll of Magnet Wire (C) 

I Roll of Masking Tape (D) 

1 Galvanized Wire (E) 

Varnish (F) 

1 Bolt (G) 

1 Nut (H) 

2 Washers (I) 

1 Wood (J) 

1 Wood (K) 



Dimensions 
12 cm x 7.5 cm 
#24, 250 g 
#20, 60 g 

#12, 30 meters 



. 5 cm diameter, 14 
cm long 

0.5 cm internal 
diameter 

4 cm external 
diameter 

20 cm x 15 cm x 1.5 cm 
15 cm x 3 cm x 2 cm 



Bolts (L) 
Nuts (M) 
Insulation Tape (N) 



b. Construction 
(1) Coils 




Winding Block 



Razor Lines 




Cardboard 
Holder (A) 



Masking 
Tape 



2 . 5 cm long, . 3 cm 
diameter 

0.3 cm internal 
diameter 



Cut a piece of wood (10 cm x 3 
cm x 3 cm) to serve as a 
winding block for the primary 
and secondary coils. Take 
the sheet of cardboard (A) and 
use a razor blade to score 
parallel lines on it at 3 cm 
intervals so that it may readily 
be bent to the shape of the 
wooden block. 



Wrap the cardboard around the 
block, fastening the two loose 
edges together with masking 
tape (D), thus producing a 
cardboard holder on which to 
wind the coils. 



Winding 

Block 



Wind 800 turns of #24 magnet 
wire (B) , approximately 250 g, 
on to the cardboard holder to 
make the primary coil, leaving 
about 10 cm of wire free at 



Masking 

Tape 




Free Ends 
of Coil 



Secondar 
Endpieces 



Cardboard 

Holder. (A) 



Last Layer 
of Coil (B) 




Cardboard 
/Holder (A) 

Primary Coil (B) 



Secondary 
Coil (C) 



Mas king 
Tape 



Primary 
Endpieces 



both ends. To do this a system 
of winding such as that described 
under IX/A2 should be adopted. 
(A variation is described in th 
notes below.) Wind the turns on 
to only the middle 6 cm or so 
of the cardboard holder. After 
winding each additional layer 
of turns, temporarily remove 
the cardboard holder (and turns) 
from the winding block, and 
cover the turns with masking 
tape. This not only holds the 
new layer of turns in position, 
but also insulates it from the 
next layer to be added. 

Next, take wire (C) , and wind 
40 turns, approximately 60 g, 
on top of the primary coil 
following the same procedures 
described for the primary coil, 
but in this case making each 
layer only about 3.5 cm long, 
instead of 6 cm. As before, 
insure that each layer of 
turns is insulated from the 
next with masking tape, and 
that some 10 cm of wire is left 
free at both ends of the coil. 
The newly added coil is appro- 
priately labeled the secondary 
coil. 



(2) Core 




' Galvanized 
Iron Wire (E) 



Dolt (G) 




Nut (H) 



C§gb«- Washer (I) 



-Washer (I) 



Cut the galvanized iron wire 
(E) into a series of 20 cm 
lengths. Dip these in varnish 
(F), and then lean them against 
a vertical surface to dry, in 
such a way that varnish is not 
removed from the wire in the 
process of drying. One to two 
days will be required for the 
varnish to dry. 

Take the dry wires one at a 
time, and bend them through, 
and around, the coil so that 
the wire ends just touch, or 
overlap, one another. If the 
wire is too long, cut the ends. 
Continue adding the iron wires 
to the coil in the same way, 
distributing the wires equally 
on each face of the coil, until 
the coil is almost full of iron 
wire. However, leave enough 
space to squeeze bolt (G) 
through the middle of the wire 
core. 

Slide bolt (G) through the 
middle of the iron wires. 
Washers (I) should be fitted on 
either end of the bolt, and 
the whole kept in position with 
a suitable nut (H) . 



Iron Wires (E) 



-144- 



(3) Base 




Make the base from wood (J) . 
Drill a hole (diameter 0.5 cm) 
through the center, and attach 
the coil and core to the base 
with the help of the bolt (G) 
through the middle of the core. 
Make an inset in the bottom of 
the base to accommodate the bolt- 
head. 



Wood (J) 




1, 



Primary Terminals 



'Secondary Terminals 



Coil and 
Core 




Wood (K-) 



Holes for 
Terminals 



Use the bolts (L) and nuts (M) 
to make four terminals (as 
described under VIII/A2) . Fit 
two at one end of the base to 
serve as secondary terminals, 
and attach the ends of the 
secondary coil to these, after 
cleaning the ends of the wire 
with sandpaper. Fit the other 
two terminals at the other end 
of the base to serve as the 
primary terminals. Attach the 
ends of the primary coil to the 
terminals after cleaning the 
ends of the wire with sandpaper. 
Remembering that the primary 
coil will be connected to the 
mains (120 volts) it is impor- 
tant to insure good insulation 
of all primary terminals and 
wires. Therefore, cover each 
of the wires from the primary 
coil to the relevant terminal 
with electrical insulation 
tape (N) . In addition make a 
safety cover from wood (k) . 
Simply cut holes (2 cmd ee p, 



1 cm diameter) in the under- 
surface of the wood to accommo- 
date the terminals, and set the 
wood on the base so that it 
covers the terminals. 



C. Notes 



Winding 
Block 



Screw 




Hand 
Drill 



(i) A convenient way of winding the coils is to use a hand d]M- and windjing 
block. Clamp the tiand drill horizontally above the bench surface, and hold 
winding block horizontally in the drill chuck with the help of a screw fixed 
firmly in the end of the winding block. If a cardboard sleeve is fitted over the 
winding block, the wire may be wound on the sleeve, and the latter subsequently 
removed complete with newly wound coil. 

(ii) The transformer made and tested here actually had 800 turns on the primary 
and 43 turns on the secondary. The voltage output was noted to be 6.6 volts when 
the current load was at a minimum, and that it fell to 5.5 volts as the load 
increased to 4 amps. At the same time the efficiency of the transformer increased 
from 32% at 6.6 volts to 45% at 5.5 volts. 

(iii) Tested under a continuous load of 4 amps, the temperature of the core rose 
to 69°C over a period of 50 minutes , at which point the load was cut off to prevent 



serious overheating of the core. The data, indicated below, suggested that this 
transformer could be used continuously under a load of 3 amps, but with a load of 
4 amps it should not be used for periods exceeding 30 minutes at any given time. 



Room 


output 


output 


Running 




Core 


Temperature 


Voltage 


Amperage 


Time 




Temperature 


°C 


Volts 


Amps 


Minutes 




°C 


24 


5.5 


4 



20 
40 
50 




24 
50 
64 
68 








Testing 


stc 


pped after 50 min 



Under the smaller load of 2.8 amps the core heated up more slowly, 
stabilizing at 62°C. 



'Room 


output 


output 


Running 


Core 


Temperature 


Voltage 


Amperage 


Time 


Temperature 


°C 


Volts 


Amps 


Minutes 


°C 


24 


6.0 


2.8 



20 
40 
60 


24 
46 
56 
62 



1 cm diameter) in the under- 
surface of the wood to accommo- 
date the terminals, and set the 
wood on the base so that it 
covers the terminals. 



c. Notes 



Winding 
Block 



Screw 




Hand 
Drill 



(i) A convenient way of winding the coils is to use a hand drill and winding 
block. Clamp the tiand drill horizontally above the bench surface, and hold a 
winding block horizontally in the drill chuck with the help of a screw fixed 
firmly in the end of the winding block. If a cardboard sleeve is fitted over the 
winding block, the wire may be wound on the sleeve, and the latter subseguently 
removed complete with newly wound coil. 

(ii) The transformer made and tested here actually had 800 turns on the primary 
and 43 turns on the secondary. The voltage output was noted to be 6.6 volts when 
the current load was at a minimum, and that it fell to 5.5 volts as the load 
increased to 4 amps. At the same time the efficiency of the transformer increased 
from 32% at 6 . 6 volts to 45% at 5 . 5 volts. 

(iii) Tested under a continuous load of 4 amps, the temperature of the core rose 

to 69°C over a period of 50 minutes, at which point the load was cut off to prevent 



serious overheating of the core. The data, indicated below, suggested that this 
transformer could be used continuously under a load of 3 amps, but with a load of 
4 amps it should not be used for periods exceeding 30 minutes at any given time. 



Room 


output 


output 


Running 




Core 


Temperature 


Voltaqe 


Amperage 


Time 




Temperature 


°C 


Volts 


Amps 


Minutes 




°C 


24 


5.5 


4 



20 
40 
50 




24 
50 
64 
68 








Testing 


stc 


pped after 50 min 



Under the smaller load of 2.8 amps the core heated up more slowly, 
stabilizing at 62°C. 



Room 


output 


output 


Runnj 


_ng 


Core 


Temperature 


Voltaqe 


Amperage 


Time 




Temperature 


°C 


Volts 


Amps 


Minutes 


°C 


24 


6.0 


2.8 



20 
40 




24 
46 
56 








60 




62 



-147- 



A2 . Transformer, Sheet Iron Core (12 volt output, 120 volt mains ) 



(1) Coils 



(2) Core 




(3) Vertical 
Support 



a. Materials Required 




Components 


Qu 


(1) Coils 


1 




: 

l 
l 



(2) Core 



60 



(3) Vertical Support 1 



(4) Base 



Items Required 
Sheet of Cardboard (A) 
Roll of Magnet Wire (B) 
Roll of Magnet Wire (C) 
Roll of Masking Tape (D) 

Galvanized Iron Sheets 
(more sheets required if 
thinner sheeting is used' 



Bolts (F) 



5 Nuts (G) 



Varnish (H) 

Galvanized Iron or 
Aluminum Sheet (I) 

Wood (J) 
Wood (K) 
Bolts (L) 

Nuts (M) 



Dimensions 
12 cm x 7.5 cm 
#24, 250 g 
#20, 100 g 



E) 13 cm x 10 cm x 

0.05 an 

0.3 cm diameter, 
3.5 cm long 

0.3 cm internal 
diameter 



47.5 x 5 x 0.02 all 

30 cm x 15 cm x 1.5 cm 

15 cm x 3 cm x 2 cm 

2.5 cm long, 
0.3 cm diameter 

0.3 cm internal 
diameter 



-14] 



Insulation Tape (N) 



b. Construction 
(1) Coils 



(2) Core 



Crosspiece 



W-shaped Core 

T 




o Bolt Holes 



Follow the instructions given 
with the foregoing transformer 
(VII/A1) for the construction 
of the coils. Make a form, on 
which to wind the coils, from 
the cardboard sheet (A) , and 
wind BOO turns of magnet wire 

(B) on to the form to make the 
primary coil. Then wind BO 
turns (not 40) of magnet wire 

(C) on to the coil to make the 
secondary coil. 

Stack the sheets of galvanized 
iron (E) one on top of the 
other, until they make a pile 
2.B cm thick. This will reguire 
55, or more, sheets, dependent 
on the thickness of each. Then 
cut each sheet as illustrated 
to form a W-shaped core piece 
and a rectangular crosspiece. 



Stack the newly cut plates back 
on top of each other, and drill 
five bolt holes (diameter 0.4 cm) 
through the plates. A drill 
press is preferred for this pur- 
pose, but it is possible to 
hand drill each plate separately. 
Use nuts (G) and bolts (F) to 




Primary 
Endpieces 



Secondary 
Endpieces 



fasten the plates of the cross- 
piece and core together. 

Take a file to smooth off the 
rough edges of the newly made 
core. It is important that the 
finished surfaces should insure 
good contact between the top 
of the W-shaped core and the 
crosspiece . 

Now take the plates apart, paint 
varnish (H) on each in turn, 
reassembling the plates while 
still wet. The varnish acts as. 
an insulator, which reduces 
eddy currents, and hence heating 
effects, within the core. The 
core may take one or two days 
to dry. 

Assemble the coils on the W- 
shaped core, using paper or wood 
wedges if necessary to insure 
the coil is held firmly on the 
central upright of the core. 



(3) Vertical Support 



Screw Holes 



Guidelines 



5.0] 



A 



Z\ — { _v_ l. 

- a A --- - 



l« H*- 



-»l« * 



r-3.0 



5.0 13.5 10.5 13.5 5.0 



sC. 



(4) Base 




Secondary 
Terminals 



Vertical 
Support 



Safety 
Cover 



Use galvanized iron or aluminum 
sheeting (I) to make the verti- 
cal support. Cut it to the 
dimensions indicated, and bend 
it into the shape of a bridge. 
Drill two holes (diameter 0.3 
cm) in either foot of the bridge 
so that the support may subse- 
quently be attached to a base 
with screws . 



Make a base for the transformer 
out of wood. (J) . Fit the 
vertical support snugly over 
the core and coils, and attach 
the support to the middle of 
the base with screws. 

Use bolts (L) and nuts (M) to 
make four terminals [as described 
under VIII/A2, Component (4)]. 
Fit two at one end of the base 
to serve as secondary terminals, 
and attach the ends of the 
secondary coil to these after 
cleaning the ends of the wire 
with sandpaper. Fit the other 
two terminals at the other end 
of the base to serve as the pri- 
mary terminals. Attach the ends 
of the primary coil to the 
terminals after cleaning the 
ends of the wire with sandpaper. 
Remembering that the primary coil 
will be connected to the mains 
(120 volts), it is important to 
insure good insulation of all 



-151- 




Wood (K) 



Holes for 
Terminals 



primary terminals and wires. 
Therefore, cover each of the 
wires from the primary coil to 
the relevant terminal with elec- 
trical insulation tape (N) . 

In addition, make a safety cover 
for the primary terminals from 
wood (K) . Simply cut holes 
(2 cm deep, 1 cm diameter) in 
the undersurface to accommodate 
the terminals, and set the wood 
on the base so that it covers 
the terminals. 



c. Notes 

(i) The voltage output of the secondary coil of the transformer will be at a 
maximum when the current load is at a minimum. In this case it was noted that 
the output voltage fell from 12 volts at 1 amp to 11 volts at 4 amps. At the same 
time the efficiency of the transformer increased from 47% at 12 volts to 62% at 
11 volts. 

(ii) Tested over a period of 90 minutes under a continuous load of 4 amps, the 
temperature of the core remained well within acceptable limits. The following 
data indicates the degree of heating somewhat more explicitly. 



Room 


output 


output 


Running 


core 


Temperature 


Voltage 


Amperage 


Time 


Temperature 


°c 


Volts 


Amps 


Minutes 


°C 


24 


10.8 


4 



20 

40 
60 
90 


24 
52 
56 
59 
59 



Under smaller loads the core heats up more slowly, but observations tended 
to suggest that the ultimate equilibrium temperature achieved (59°C) was the same 
as with the heavier load. (See table on next page.) 



— 












Room 


output 


output 


Runni 


ng 


Core 


Temperature 


Voltaqe 


Amperaqe 


Time 




Temperature 


°c 


Volts 


Amps 


Minutes 


°C 


24 


11 


3 



20 
40 
60 




24 
44 
52 
59 



-13J- 



A3 . Transformer, Variable Output (120 volt mains) 




(4) Base 



a. Materials Required 
Components 
(1) Coils 



1) Coils 



Qu 

1 

: 



(2) Core 



(3) Vertical Support 1 



(4) Base 



(3) Vertical 
Support 



Items Required 
Cardboard Sheet (A) 
Roll of Maqnet Wire (B) 
Roll of Maqnet Wire (C) 
Maskinq Tape (D) 

Galvanized Iron Sheets (E) 
(more sheets required if 
thinner sheetinqis used) 

Bolts (F) 
Nuts (G) 

Can of Varnish (H) 

Galvanized Iron or Aluminum 
Sheet 

Wood (J) 
Wood (K) 



Dimensions 

13.0 cm x 11.5 cm 

#24, 250 q 

#20, 250 q 



17 cm x 10 cm x 
0.05 cm 

0.3 cm diameter, 
3.5 cm lonq 

0.3 cm internal 
diameter 



55 . 5 cm x 5 cm x 
0.02 cm 

30 cm x 20 cm x 1.5 cm 
2 cm x 3 cm x 2 cm 



-154- 



b. Construction 



(1) Coils 




Winding 
Block 



Sheet 



Bolts (L) 



Nuts 



2 . 5 cm long, . 3 cm 
d 1 ameter 

. 3 cm internal 
di ameter 



Roll of Insulation Tape (N) 



r* 


13 


**i 


<- _l 


1 1 




3.25 | 

i 

1 

i 
t 


I 1 

1 1 

1 I 

1 1 




V 







Razor Line 




Cardboarc 

Form (A) 



Primary 
Coil (B) 



Masking Tape 



Cut a piece of wood (14 cm x 
3.2 cm x 3.2 cm) to serve as 
a winding block for the primary 
and secondary coils. Take the 
thin sheet of cardboard (A) 
and use a razor blade to score 
parallel lines on it at intervals 
of 3.25 cm, so that the card- 
board may readily be bent around 
the wooden block. 

Wrap the cardboard sheet around 
the block, fastening the loose 
edges together with masking 
tape (D), thus producing a card- 
board form on which to wind the 
primary and secondary coils . 

To make the primary coil, wind 
720 turns (approximately 250 g) 
of magnet wire (B) , onto the 
cardboard form. Each layer of 
turns will be 10 cm long. Place 
masking tape between each layer. 
The actual method of winding is 
described under VII/A1. 



Free Ends 
of Coil 



To make the secondary coil, wind 
180 turns (approximately 2 5 g) 
of magnet wire (C) on top of the 
primary coil in the usual way 
(leaving a free end about 20 cm 
long at the start) . However, 




Masking Tape 

■Tap 2 
Tap 1 



Secondary 

Coil (C) 



. Free End of 
Secondary 



2.5 




1 7* 

Bolt Holes< 



Smooth Surfaces 



14.5 




I* ►! 

2.2 1.4 2.8 1.4 2.2 

W-shaped 
Core 



halt after every 30 turns to 
make a tap. (The latter is 
made by taking the next 40 cm 
of wire, folding it to make a 
double strand, and twisting it 
around itself.) Then continue 
for another 30 turns before 
making a further tap, again 
with a 40 cm length of wire. 
It is very important to make 
the taps at the corners of the 
secondary coil, otherwise they 
will interfere with the place- 
ment of the coil on the core. 
Each layer of turns should be 
covered in the usual way with 
masking tape to insulate it 
from the next layer. In all, 
there should be taps after 
30, 60, 90, 120 and 150 turns, 
and a free end (20 cm long) 
after 180 turns. 

Stack the galvanized iron sheets 
(E) on top of the other until 
the pile is 2.8 cm thick. This 
will require 55, or more, 
plates, dependent on the thick- 
ness of the sheet. Then cut 
each of the sheets as illustrated 
to form a W-shaped plate and a 
rectangular crosspiece. 

Stack the newly cut plates back 
on top of each other, and drill 
5 bolt holes (diameter 0.4 cm) 
through the plates. A drill 
press is preferred for this 
purpose, but it is possible to 
hand drill each plate separately. 
Use nuts (G) and bolts (F) 



Primary 
Endpieces 



Secondary 
Endpiece 




to fasten the plates of the 
crosspiece and core together. 

Take a file to smooth off the 
rough edges of the newly made 
core. It is important that the 
finished surfaces should insure 
good contact between the top of 
the W-shaped core and the cross- 
piece. 

Now take the plates apart, and 
cover each in turn with varnish 
(H) , reassembling the plates 
while still wet. The varnish 
acts as an insulator, which 
reduces eddy currents, and hence 
heating effects, within the 
core. The core may take one or 
two days to dry. 

Assemble the coils on the 
W-shaped core, using paper or 
wood wedges if necessary to 
insure the coil is held firmly 
on the central upright of the 
core. 



Core 



Secondary 
Endpiece 



(3) Vertical Support 



Guidelines 
for Bends 



5.0 



I -41 



5.0 






£x 



17.5 



10.5 






-J 



^ 3.0 



17.5 



5.0 



Use galvanized iron or aluminum 
sheeting (I) to make the verti- 
cal support. Cut it to the 
dimensions indicated, and bend 
it to the shape of a bridge. 
Drill two holes (diameter 0.3 
cm) in either foot of the bridge 
so that the support may subse- 
guently be attached to a base 
with screws . 



nv 



T~^ 



Screw Holes 




Secondary 
Terminals 



Safety 
Cover (K) 



Make a base for the transformer 
out of wood (J) . Fit the 
vertical support snugly over 
the core and coils, and attach 
the support to the middle of 
the base with screws. 



Wood (J) 




-v 



Coils 



Taps 



Core 




Wood (K) 



Holes for 
Terminals 



Use bolts (L) and nuts (M) to 
make nine terminals [as 
described under VII/AZ, Component 
(4)]. Fit seven at one end of 
the base to serve as secondary 
terminals, and attach the ends 
of the secondary coil and the 
taps to these after cleaning the 
ends of the wire and taps with 
sandpaper. Cover the wires with 
insulation tape (N) or tubing to 
prevent any possibility of a 
short. Fit the other two termi- 
nals at the other end of the 
base to serve as the primary 
terminals. Attach the ends of 
the primary coil to the terminals 
after cleaning the ends of the 
wire with sandpaper. Remembering 
that the primary coil will be 
connected to the mains (120 
volts), it is important to insure 
good insulation of all primary 
terminals and wires. Therefore, 
cover each of the wires from the 
primary coil to the relevant 
terminal with electrical insula- 
tion tape. 

In addition, make a safety cover 
for the primary terminals from 
wood (K) . Simply cut holes 
(2 cm deep, 1 cm diameter) in 
the undersurface to accommodate 
the terminals, and set the wood 
on the base so that it covers 
the terminals. 



c. Notes 

(i) Do not expect the output voltages to be exactly 5, 10, 15 volts and so on, 
With the apparatus produced and tested here the output voltages, observed by com- 
bining any one tap with the coil endpiece, were 4.5, 10.0, 15.0, 21.0, 26.3 and 



-159- 



31.0 volts when the primary voltage was 121 volts. 

(ii) The transformer was tested using the 10, 20 and 30 volt outputs. As 
expected, it was noted that the transformer operated more efficiently at the higher 
voltages . 

The voltage output from any given pair of terminals was observed to fall as 
the current output increased. Actual results are tabulated below. 



120 . . 
volts S- InpUt 
AC 




Output Taps 


' 30 volts 










Input 






output 






*Power 

Watts 


I 
Amps 


V 

Volts 


R 
Ohms 


*Power 
Watts 


Efficiene 
% 


46 


1.00 


28.4 


28.4 


28.40 


62 


52 


1.25 


28.0 


22.4 


35.00 


67 


59 


1.50 


27.5 


18.3 


41.25 


70 


68 


1.75 


27.0 


15.4 


47.25 


69 


75 


2.00 


26.5 


13.2 


53.00 


71 


82 


2.25 


26.0 


11.5 


58.50 


71 


90 


2.50 


25.5 


10.2 


63.75 


71 


97 


2.75 


25.0 


9.1 


68.75 


71 


105 


3.00 


24.0 


8.0 


72.00 


69 



* Power was measured directly with wattmeters. 



Output Taps = 20 volts 



Input 






output 






*Power 
Watts 


I 

Amps 


V 

Volts 


R 
Ohms 


*Power 

Watts 


Efficiency 
% 


33 


0.75 


19.5 


26.0 


14.6 


44 


3a 


1.00 


19.2 


19.2 


19.2 


50 


43 


1.25 


19.0 


15.2 


23.7 


55 


4a 


1.50 


la. 5 


12.3 


27.7 


5a 


52 


1.75 


la. 3 


10.4 


32.0 


61 


56 


2.00 


la.O 


9.0 


36.0 


64 


61 


2.25 


17.7 


7.9 


39. a 


65 


66 


2.50 


17.5 


7.0 


43.7 


66 


71 


2.75 


17.0 


6.2 


46.7 


66 


76 


3.00 


16.5 


5.5 


49.5 


65 



Output Taps 


= 10 volts 










Input 






output 






*Power 
Watts 


I 

Amps 


V 

Volts 


R 
Ohms 


*Power 

Watts 


Efficienc} 

% 


22 


0.50 


9 . 


18.0 


4.5 


20 


24 


0.75 


a. a 


11.7 


6.6 


27 


26 


1.00 


a. 7 


a. 7 


a. 7 


33 


29 


1.25 


8 . 6 


6.9 


10.7 


37 


31 


1.50 


a.4 


5.6 


12.6 


41 


34 


1.75 


a. 3 


4.7 


14.5 


43 


36 


2.00 


a.l 


4.0 


16.2 


45 


3a 


2.25 


a.O 


3.5 


18.0 


47 


40 


2.50 


7. a 


3.1 


19.5 


49 


43 


2.75 


7.7 


2. a 


21.2 


49 


45 


3.00 


7.6 


2.5 


22. a 


51 



* Power was measured directly with wattmeters. 



(iii) Some heating of the transformer was noted, but this appeared to be within 
acceptable limits. Hence, when a current of 3 amps was drawn from the maximum 
voltage taps (30 volts) the temperature of the transformer core did not rise beyond 
60° Centigrade. 

Output Taps = 30 volts 
output = 3 amps at 24 volts 
Room Temperature = 2 4 °C 



Running 

Time 
(Minutes) 


Core 

Temperature 
(Degrees Centigrade) 





27° 


C 


5 


38° 


c 


10 


48° 


c 


15 


49° 


c 


20 


51° 


c 


25 


53° 


c 


40 


56° 


C 


50 


58° 


c 


60 


59° 


c 



B. RECTIFIERS 



Bl. Sodium Bicarbonate Rectifier (2 Plate) 




(1) Cell 
Containers 



(5) Wiring 



(3) Plates Support 



ates 



(2) Base 



a. Materials Required 

Components q u Items Required 

(1) Cell Containers 4 Glass Jars (A) 



(2) Base 



1 Plywood Sheet (B) 

1 Wood Strip (C) 

2 Wood Strips (D) 
4 Wood (E) 



Dimensions 

Approximately 300 ml, 
10 cm diameter 

22 cm x 22 cm x 0.5 cm 
22 cm x 2 cm x 2 cm 
10 cm x 2 cm x 2 cm 
2cmx2cmxlcm 



(3) Plates Support 



(4) Plates 



2 Wood (F) 

2 Wood (G) 

4 Lead Sheets (H) 

4 Aluminum Sheets (I) 

8 Bolts (J) 

a Nuts (K) 



15 cm x 1.5 cm x 1.5 cm 
12 cm x 1.5 cm x 1.5 cm 

6.5 cm x 5 . cm x 
0.02 cm 

6.5 cm x 5.0 cm x 

0.02 cm 

0.3 cm diameter, 
2.5 cm long 

0.3 cm internal diameter 



(5) Wiring 

c. Construction 

(1) Cell Containers 




16 Washers (L) 



4 Filter Papers (M) 

1 Saturated Solution of 
Sodium Bicarbonate (N) 



Roll of Magnet Wire (0) 



0.3 cm internal 
diameter, approximately 

5.5 cm x 5.5 cm 

1 liter 

#24 



To make a cell container, take 
jar (A) , and use a hot nichrome 
wire (CHEM/I/F2) to cut the top 
off the jar some 6 cm above the 
base. Repeat the process with 
three more jars. 



(2) Base 



^Se.J 

/ * 
1 

\ / 






«» 


S^ — . 

/ \ 
/ \ 

1 1 

\ (E) (D)-^-, 


(C) N 
/ \ 

* (E) x / 



Nail wood strips (C,D) to the 
top of the plywood sheet (B) 
so as to divide it into four 
equal portions. Nail the wood 
strips (E) at the corners of 
the plywood in such a way that 
the four cell containers, placed 
in the appropriate quarters, 
will be held in position on the 
plywood base. 



Plywood Base (B) 



(3) Plates Support 



(f 



7* 



(H) 



-(G) 



(H) 



4 



Bolt Holes 



(4) Plates 



1.0 



0.5: 



/ 



Hole- 



Plate 



t 1.5 



5.0 



I* 5.0 "I 



Nut (K) 
Support (F/G) 



Plate (H 




Washers (L) 



Use wood Strips (F) and (G) 
to make the frame of the plate 
support. Drill two bolt holes 
(0.3 cm diameter) in each side 
of the support, such that the 
holes in any one side are 4 cm 
apart, and are equidistant 
from the center of the side. 



Cut a plate out of lead 
sheeting (H) and another out 
of aluminum sheeting (I) to 
the dimensions shown. Drill 
a hole (0.3 cm diameter) in 
the projecting portion of 
each plate. 



Attach the lead plate to the 
plate support with the help 
of bolt (J) , nut (K) and 
washers (L) placed either 
side of the plate. 



Attach the aluminum plate to 
the plate support in the same 
way, but so that the aluminum 
plate lies on top of the lead 



Plate Support (f/g) 




Filter 
Paper (M) 



Aluminum 
Plate (I) 



(5) Wiring 



AC 
Source O 




plate. Place the sheet of filter 
paper (M) between the two plates, 
thus insulating one from the 
other, 

Cut three more lead plates and 
three more aluminum plates, 
and make identical plate pairs 
(insulated with filter paper) 
for the three remaining sides 
of the plate support. 

Rest the plate support on the 
four cut jars, such that one 
pair of plates is suspended 
in each jar. 

Almost fill each jar with a 
saturated solution of sodium 
bicarbonate (N),that is baking 
soda, and add a little extra 
sodium bicarbonate to each 
cell to insure that the solution 
remains saturated during use. 

Use copper wire (0) to connect 
the plates of the four cells 
together, as indicated in the 
diagram. The cells have the 
simple property of permitting 
electrons to flow only in one 
direction, from aluminum to 
lead, and when connected as 
indicated to an AC source a 
rectified output is obtained. 
The type of output obatined 
with AC sources of 12 volts 
and 25 volts is indicated in 
the notes . 



— ^ Lead Plate 

I Aluminum Plate 



c. Notes 



(i) The AC voltage supply may be taken from the transformer already described 
(VII/A3) . A series of tests were conducted on the rectifier produced here, after 
it had been running for one hour. The results are tabulated below. 

(ii) With a variable resistance (R) connected across the DC output it will be 

noted that the output voltage 
(V r ) fell off as the resistance 
decreased. [A very small 
proportion of the fall in 
voltage may be attributed to 
the drop in voltage (V t ) from 
the transformer.] 




AC Su)ply= 15 volt taps 












Load 




Transformer 


Output 


Rectifier Outpi 


t 


Efficiency 


R 
Ohms 


v t 

Volts 


h 

Amps 


W t 

Watts 


v r 
Volts 


Amps 


w r 
Watts 


% 


820 


15.7 


0.10 


1.57 


8.2 


0.01 


0.08 


5.2 


800 


15.6 


0.11 


1.71 


8.0 


0.01 


0.08 


4.7 


390 


15.6 


0.15 


2.34 


7.8 


0.02 


0.16 


6.7 


172 


15.5 


0.20 


3.10 


6.9 


0.04 


0.28 


8.9 


98 


15.5 


0.21 


3.26 


5.9 


0.06 


0.35 


10.8 


84 


15.4 


0.25 


3.86 


5.9 


0.07 


0.41 


10.7 


70 


15.3 


0.30 


4.59 


5.6 


0.08 


0.45 


9.8 


60 


15.3 


0.30 


4.59 


5.4 


0.09 


0.49 


10.6 


52 


15.3 


0.30 


4.59 


5.2 


0.10 


0.52 


11.3 


42 


15.2 


0.30 


4.56 


5.0 


0.12 


0.60 


13.2 


31 


15.1 


0.35 


5.28 


4.6 


0.15 


0.69 


13.1 


21 


15.1 


0.45 


6.80 


4.2 


0.20 


0.84 


12.3 


11 


15.0 


0.61 


9.15 


3.4 


0.31 


1.05 


11.5 


9 


14.9 


0.75 


11.18 


3.2 


0.37 


1.18 


10.6 


6 


14.8 


0.95 


14.06 


2.8 


0.45 


1.26 


8.9 


5 


14.5 


1.05 


15.23 


2.6 


0.50 


1.30 


8.5 


3 


14.0 


1.35 


18.90 


1.9 


0.68 


1.29 


6.8 



-167- 



AC Swjfo 1 'Q= t .3 t; Y\yi 1 t taps 



1 

Load 


Transformer 


Output 


Rectifier Output 


Efficiency 


R 
Ohms 


V t h 

Volts Arrps 


W t 

Watts 


V 
Volts 


Arrps Watts 






1,850 


25.9 0.48 


12.43 


la. 5 


0.01 0.18 


1.5 


910 


25.9 0.48 


12.43 


la. 2 





02 0.36 


2.9 


583 


25.9 0.50 


12.95 


17.5 





03 0.53 


4.1 


435 


25.9 0.50 


12.95 


17.4 





04 0.70 


5.4 


275 


25.8 0.55 


14.19 


16.5 





06 0.99 


7.0 


200 


25.8 0.60 


15.48 


16.0 





08 1.28 


a. 3 


97 


25.2 0.70 


17.64 


14.5 





15 1.45 


a. 2 


a9 


25.1 0.75 


la. 82 


14.2 





16 2.27 


12.1 


78 


25.1 0.78 


19.58 


14.0 





18 2.52 


12.9 


69 


25.0 0.80 


20.00 


13.8 





20 2.76 


13.8 


61 


25.0 0.85 


21.25 


13.5 





22 2.97 


14.0 


50 


24.8 0.95 


23.56 


13.0 





26 3.38 


14.4 


39 


24.5 1.05 


25.73 


12.5 





32 5.00 


19.4 


30 


24.0 1.22 


29.28 


12.0 





40 4.80 


16.4 


20 


23.5 1.52 


35.72 


11.0 





55 6.05 


16.9 


10 
i 


22.2 2.15 


47.73 


9.0 





88 7.82 


16.4 



(iii) The current output of the rectifier was very low, but was noted to increase 
when the voltage from the transformer was increased. Thus with a resistance of 
10 ohms in the external circuit the DC current produced was 0.34 or 0.88 amps 
according to whether the rectifier was connected to the 15 or 25 volt taps on the 
transformers . 

(iv) The rectifier was extremely inefficient in its use of power. The maximum 
efficiency on the 15 volt taps was noted to be 13% and on the 25 volt taps to be 
19%. 

(v) It was noted that not only did the output voltage (V r ) from the rectifier 
decrease with increasing resistance (R) , but that there was also some variation 
of the voltage (V r ) at a fixed resistance (R) with the passage of time. These 
factors suggest that although the apparatus is capable of producing a DC current, 
the latter is not suitable for quantitative (as opposed to qualitative) experi- 
mentation. 



B2 . Silicon Rectifier 




(1) Base 



(2) Rectifiers and 
Supports 



(3) Electrical 
Connections 



a. Materials Required 



Components 


Qu 


Items Required 


(1) Base 


1 


Wood (A) 


(2) Rectifiers 


and 4 


Silicon Rectifier 


Supports 




Diodes (B) 




4 


Brass Bars (C) 


(3) Electrical 


2 


Brass Strips (D) 


Connections 


1 


Brass Strip (E) 




4 


Bolts (F) 




8 


Nuts (G) 



1 Copper Wire (H) 



b. Construction 



(1) Base 

(2) Rectifiers and Supports 




Use wood 



Dimensions 

15 cm x 10 cm x 2 cm 

1N1341 

7 cm x 2 cm x . 3 cm 
5 cm x 1 cm x . 5 cm 

5 cm x 3 cm x . 5 cm 

0.3 cm diameter, 
3.5 cm long 

0.3 cm internal 
diameter 

#20, 40 cm long 
(A) as the base. 



Rectifier Diode (B) 



Purchase four silicon rectifier 
diodes (B) from a radio shop or 
electrical supply house. Ask 
for a rectifier identified as 
a 1N1341. This will be capable 
of handling a peak reverse 



Diode (B) 




voltage of 50 volts, a continuous 
forward current of 6 amps and a 
maximum surge of 30 amps. 



Support (C) 





A 




&r- 




^ir 4 




l T J N 


\ 




€> 











A 




A 






" u ' 




u 






© 




e 















Diode (B) 



'Support (C) 



3ase (A) 



Take a brass bar (C) and bend 
it at right angles, 4 cm from 
one end, to form an L-shaped 
support. Drill a hole (0.5 cm 
diameter) in the middle of the 
long upright of the support and 
a hole (0.3 cm diameter) in the 
base of the support. Screw one 
of the rectifier diodes in the 
upright portion of the support. 
Attach the three remaining 
diodes (B) to three identical 
supports (C) in the same way. 
Attach the four supports to the 
base (A) . it should be noted 
that the supports also act as 
heat sinks, removing heat that 
is generated within the diodes. 
It is for this reason that the 
support is made from a thick 
metal bar. 



-170- 



(3) Electrical Connections 



Terminals (F/G 




q 



Brass Strips (D) 
-Brass Strip (D) 



Take the two brass strips (D) 
and drill a hole (0.3 cm 
diameter) close to the end of 
each. Insert the strips under 
the supports (C) at one end of 
the base as indicated. Use 
bolts (F) and nuts (G) to make 
four terminals (F/G) as 
described under VIII/A2,Com- 
ponent (4) . Fit two of the 
terminals on the base so that 
each is connected to a brass 
strip by means of the appro- 
priate hole. 



Terminal Hole 




(F,G) 



Brass Strip (E) 



Cut an L-shaped strip out of 
brass sheet (E) . Drill a hole 
(0.3 cm diameter) in the end of 
the shorter arm, and fit the 
longer arm beneath the two 
remaining supports so that they 
are connected electrically. Fit 
Terminals the two remaining term 

(F/G) to the end of the base, 

so that one is connected to the 
L-shaped strip. 



«« 5.0 •' i 

jniiiiiniiiiiHiiiinnnnn 1.0 




Brass strip (E) 



l g Terminal Hole 



AC Terminals 




Solder 
Contacts 



Copper 
Wire 



Solder 
Contacts 



Take the copper wire (H) and 
connect the silicon diodes as 
illustrated. It will be 
necessary to solder the wire 
on to the ends of the diodes, 
and particular care should be 
taken to avoid overheating, 
since this can destroy the 
diodes . 



DC Terminals 



c. Notes 



(i) The rectifier produced is represented diagrammatically here. The reader 

should compare this with the 
previous diagram, noting the 
equivalent components marked 
by letters of the alphabet. 



DC 
£"| Terminals 




(ii) With a variable resistance R connected across the DC output it will be noted 

that the output voltage (V r ) 
falls off as the resistance 
decreases, even when the 
transformer is continuously 
monitored to keep the voltage 
(V^) constant. This pattern 
of behavior is the same as for, 
the Sodium Bicarbonate Recti- 
fier (VII/B1) . However, it 
will be noted that the efficiency 
of the Silicon Rectifier varies 
from 60% to 70% and the rectified 
current is as great as 3 amps at 
5.5 volts. In this respect the 
Silicon Rectifier is a consider- 
able improvement over the Sodium 
Bicarbonate Rectifier. 




AC Supply = 10 volt taps 



Load 


Transformer 


Output 


Rect 


Lfier Output 


■ 
Efficiency 


R 


V t r t 


W t 


V 


l r W r 




Ohms 


Volts Amps 


Watts 


Volts 


Amps Watts 






110 


10.2 0.08 


0.82 


7.7 


0.07 


6 


70.4 


96 


10.2 0.09 


0.92 


7.7 


0.08 


6 


67.4 


86 


10.2 0.10 


1.02 


7.7 


0.09 


.7 


67.9 


77 


10.2 0.11 


1.12 


7.7 


0.10 


.8 


68.7 


63 


10.2 0.13 


1.33 


7.6 


0.12 


9 


68.6 


54 


10.1 0.16 


1.62 


7.6 


0.14 1 


1 


67.9 


42 


10.1 0.20 


2.02 


7.6 


0.18 1 


.4 


67.7 


31 


10.1 0.26 


2.63 


7.5 


0.24 1 


.8 


68.4 


21 


10.0 0.39 


3.90 


7.4 


0.35 2 


6 


66.7 


11 


9.9 0.77 


7.62 


7.2 


0.68 4 


9 


64.2 


9 


9.8 0.90 


8.82 


7.0 


0.80 5 


6 


63.5 


8 


9.8 1.00 


9.80 


7.0 


0.86 6. 





61.2 


7 


9.7 1.15 


11.20 


7.0 


1.00 7 





62.5 


5 


9.6 1.42 


13.60 


6.8 


1.35 8 


5 


62.3 


4 


9.4 1.68 


15.80 


6.6 


1.50 9 


9 


62.6 


3 


9.3 1.95 


18.10 


6.4 


1.75 11 


2 


61.9 


2 


8.7 3.05 


26.50 


5.8 


2.75 15 


9 


60.2 


1 


8.6 3.35 


28.80 


5.6 


3.00 16 


8 


58.3 



AC Supply = Held constant at 10 volts. 



Load 


Transformer 


Output 


Rectifier Output 


Efficiency 


R 


V t h 


W t 


V r 


r r 




Ohms 


Volts Amps 


Watts 


Volts 


Amps Watts 






128 


10.0 0.06 


0.60 


7.7 


0.06 0.46 


76.7 


95 


10.0 0.08 


0.80 


7.6 


0.08 0.60 


75.0 


63 


10.0 0.13 


1.30 


7.6 


0.12 0.91 


70.0 


38 


10.0 0.22 


2.20 


7.6 


0.20 1.52 


69.1 


25 


10.0 0.32 


3.20 


7.6 


0.30 2.28 


7.13 


19 


10.0 0.43 


4.30 


7.5 


0.40 3.00 


69.8 


15 


10.0 0.55 


5.50 


7.5 


0.50 3.75 


68.2 


12 


10.0 0.66 


6.60 


7.5 


0.60 4.50 


68.2 


9 


10.0 0.89 


8.90 


7.4 


0.80 5.92 


66.5 


7 


10.0 1.07 


10.70 


7.4 


1.02 7.55 


70.6 


6 


10.0 1.32 


13.20 


7.3 


1.25 9.13 


69.2 


5 


10.0 1.61 


16.10 


7.3 


1.51 11.02 


68.4 


4 


10.0 1.88 


18.80 


7.2 


1.75 12.60 


67.0 


3 


10.0 2.41 


24.10 


7.2 


2.25 16.20 


67.2 


2 


10.0 3.27 


32.70 


7 .1 


3.00 21.30 


65.1 



(iii) The output voltage (V r ) remains extremely steady with the passage of time, 
making this a much more suitable rectifier for quantitative experimentation than 
the Sodium Bicarbonate Rectifier. 



AC Supply = 10 volt taps 



Time 


Transformer Output 


Rectifier 


Output 


t 


V t *t 


\ 


V 


Minutes 


Volts Amps 


Volts 


Amps 


1 


9.5 1.62 


6.6 


1.50 


2 


9.5 1.62 


6 


6 


1.49 


3 


9.6 1.63 


6 


6 


1.50 


4 


9.6 1.62 


6 


6 


1.50 


5 


9.7 1.63 


6 


6 


1.51 


10 


9.7 1.63 


6 


6 


1.51 


15 


9.7 1.63 


6 


6 


1.51 


20 


9.7 1.63 


6 


6 


1.51 


25 


9 . 7 1.63 


6 


6 


1.51 


30 


9.8 1.65 


6 


6 


1.51 



-17b- 



VIII. CIRCUIT APPARATUS 

A. CELLS 

This section contains cells and simple batteries which may serve as suitable 
sources of electrical energy for typical classroom experiments. 

B. CIRCUIT COMPONENTS 



The apparatus described here is limited to such typical components as switches 
and bulb holders. 

c. RESISTORS 



Fixed and variable resistors for typical classroom experiments are described in 
this section. 

D. DYNAMO/MOTORS 

This section contains two motors which may also be used as dynamos. The first 
is a very simple device which is capable of generating only a very minute current, 
whereas the second is a much more substantial item which generates sufficient current 
to light a bulb. 



CELLS 



Al. Chemical Cell 



© 



(2) Plates 



(3) Holders 




(1 Container 



a. Materials Required 
Components 

(1) Container 

(2) Plates 



(3) Holders 



c. Construction 
(1) Container 



q u Items Required 

1 Plastic Container (A) 



1 Zinc Sheet (B) 

1 Copper Sheet (C) 

1 Steel Sheet (D) 

1 Carbon Rod (E) 
4 Brass Wire (F) 

2 Wood Holders (G) 

1 Bolt (H) 

2 Nuts (I) 



Dimensions 

Approximately 8 cm 
diameter, 8 cm deep 

5 cm x 2 cm x . 05 cm 

5 cm x 2 cm x 0.05 cm 

5 cm x 2 cm x . 5 cm 

Extracted from dry cell 

2.5 cm long, . 1 cm 
diameter 

10 cmxl cmxl cm 

0.3 cm diameter, 
1.5 cm long 

0.3 cm internal 
diameter 



Use a plastic or glass jar (A) 
as the electrolyte container. 
(A wide variety of electrolytes 



©From Reginald F. Melton, E lementary, Economic Experiments in Physics, Apparatus 
Gu'V'ift., (London: : Center for Educational Development Overseas, 1972), pp 171-112. 



(2) Plates 



Metal 
Sheet 
(B,C,D) 




Suspension fc 

Wire (F) 



/ 



Solder 



ia 



Metal 
Cap 



Carbon 

Rod (E) 



may be used, including commonly 
available vinegar and household 
salt solutions.) 

Solder a brass suspension wire 
(F) on to each of the metal 
sheets (B, C and D) . Also 
solder a similar suspension 
wire (F) to the metal cap on a 
carbon rod (E) extracted from a 
dry cell. 



(3) Holders 




Suspension. 

Wire (F) 



Suspension 

e 




Locking 
Nut (I) 

Electrical 
Lead 



Cross Section 



In each wood holder (G) , drill 
a vertical suspension hole 
(0.2 cm diameter) and a hori- 
zontal bolt hole (0.3 cm dia- 
meter) to meet the vertical 
hole. 



Inset one of the nuts (I) over 
the bolt hole with a sharp tap 
of the hammer (A little epoxy 
resin will hold the nut per- 
manently in position.) Thread 
the second nut (I) on to the 
bolt (H) to serve as a locking 
nut, and then screw the bolt 
into the bolt hole. Insert a 
suspension wire in the vertical 
hole, and clamp it in position 
by tightening the bolt. 

Electrical leads may be fastened 
under the locking nuts on the 
holders, and the cell connected 
into an electrical circuit. 



c. Notes 

(i) Any of the two plates in combination with one of the electrolytes mentioned 
above will produce an electric current. The latter may be detected by means of 
a simple galvanometer (e.g., X/Bl) . It is recommended that students compare the 
magnitudes of currents that can be produced by the various plate and electrolyte 
combinations . 



AZ. Dry Cell Holder with Cells 



© 



^ 



(3) Endpieces 



(4) Terminal 



(5) Conta 




Dry Cells 



(1) Base 



a. Materials Required 
Components 

(1) Base 

(2) Cells 

(3) Endpieces 



(4) Terminals 



q u Items Required 

1 Wood (A) 

3 Dry Cells (B) 

2 Brass Sheets (C) 

6 Screws (D) 

1 Bolt (E) 

1 Nut (F) 

4 Brass Bolts (G) 
8 Nuts (H) 

4 Magnet Wire (I) 



Dimensions 

18.5 cm x 5.5 cm x 2 cm 

1.5 volts each 

4.0 cm x 1.5 cm x 
0.3 cm 

Approximately 0.8 cm 
long 

0.4 cm diameter, 
2 cm long 

0.4 cm internal 
diameter 

0.3 cm diameter, 
2.5 cm long 

0.3 cm internal 
diameter 

#22, 15 cm long 



(Q)From Reginald F. Melton, E lementary, Economic Experiments in Physics, Apparatus 
GU'V'te. , (London : '. Center for Educational Development Overseas, 1972), pp 123-127. 



(5) Contact Plates 



b. Construction 
(1) Base 



Circular Brass Sheets (J) 



Wood (A) 



Groove 



1.5 cm diameter, 
0.05 cm thick 




Cut the base out of the soft 
wood (A) , and use a curved 
chisel to make a long groove 
(about . 5 cm deep) in the 
surface to hold the dry cells 
in position. 



(2) Cells 



(3) Endpieces 





3rass Plates (C) 



Place three dry cells (B) in 
series in the groove of the 
base. The groove should be from 
1 to 1.5 cm longer than the 
three cells placed end to end, 
thus allowing room for the 
placing of contacts between the 
cells, and for adjustment of 
the screw in one of the end- 
pieces. 

Use the brass sheets (C) for 
endpieces. Drill three small 
holes (0.2 cm diameter) at the 
base of each endpiece to facili- 
tate attachment to the base 
with the screws (D) . Place the 
dry cells on the base to 
determine the height of the 
mid-point of the dry cells, and 
then drill an inset (0.9 cm dia- 
meter, 0.15 cm deep) at this 
height in one endpiece, and a 
hole (0.4 cm diameter) at the 
same height through the other 
endpiece. Thread the newly 
drilled hole to take the 



Inset 



adjustment bolt (E) 




• 'Hole 



>*-. Screw (D) 



Dry Cell (B) 



3ase (A) 



Brass (C) 



Side View 



Brass Plate (C) 



Nut (F) 




Bolt (E) 



The latter bolt may have to be 
adjusted with the help of a 
coin, or some such device. A 
much more convenient adjustment 
bolt could be made by a 
technician, or anyone familiar 
with a metal lathe, cutting the 
head and bolt from a single 
piece of brass. The base in 
either case would be made from 
a separate nut (F), firmly 
attached to the bolt by 
damaging the threads at the end. 



Machine-made 

Adjustment Bolt 



-1BJ- 



(4) Terminals 
Terminal Nut (H) 



Machine-made 
Terminal 



1 



Bolt (G)__E 



Locking 
/ Nut (H) 




Inset 




Side View 
(Cross-section) 



Inset 



Fahnstock 
Clip 



Bare End of 
Wire Inserted 
Into Clip 




Make four terminals from the 
brass bolts (G) and nuts (H) . 
Two nuts are required for each 
terminal, one to serve as a 
locking nut and one as a ter- 
minal nut. 

Somewhat better nuts, which are 
more easily adjusted with the 
fingers, may be made with a 
metal lathe. The terminal nut 
should be 0.5 cm thick, while 
the locking nut should be much 
thinner (0.2 cm). The diameter 
of both should be 1.0 cm. 

In some localities it is cheaper 
to purchase terminals on the 
local market. Check the 
availability of such items as 
Fahnstock clips which can 
replace the above. 




Bolt (G) inset Hole 

Base, Bottom View 




Nuts (H) 



Wire (I) 



Base, Top View 



Make four insets (0.2 cm deep) 
at equal intervals underneath 
the front side of the base to 
take the boltheads of the 
terminals. Insert the four 
bolts (G) from below, through 
holes drilled through the base, 
and attach the locking nuts (H) 
and terminal nuts (H) . 

Use copper wire ( I to attach 
the end terminals to the end- 
pieces, fastening the bare ends 
of the wire beneath the terminal 
locking nuts and brass endpieces. 
Similarly attach a length of 
copper wire (I) (15 cm long) to 
each of the middle terminals. 



(5) Contact Plates 



Brass 
Sheet (J) 



Inset 




Wire (I) 



Contact 
Plate 



1.5 v Dry Cell 



Mo) 



(oj ir ' lop' 



Electrical Circuit 



Use a nail head, or punch, to 
make a central inset (1 cm 
diameter, 0.2 cm deep) in the 
two brass sheets (J) . Solder the 
two plates to the bare ends of 
the wire (I) attached to the 
two middle terminals. The 
contact plates are placed between 
the first and second, and second 
and third cells, thus enabling 
the apparatus to provide an 
external circuit with 1.5, 3.0 
or 4.5 volts according to the 
terminals connected to the 
circuit . 



C. Notes 
(i) So 



long as the adjustment bolt isnot tightened too tightly, the cells will 

remain firmly in the base groove. 
However, should any problem 
occur (e.g., due to bad align- 
ment of the adjustment screw) 
the cells could be held more 
firmly in place by means of 
clips made from packing case 
bands. 

Clip 




(ii) The dry cell holder serves as a variable source of potential providing from 
1.5 to 4.5 volts, according to the terminals connected into the circuit. 



AS. Simple Battery * 




- (2) Container 



— (1) Plates 



a. Materials Required 
Components 
(1) Plates 



(2) Container 



q u Items Required 

2 Lead Sheets (A) 

2 Lead Sheets (B) 

2 Thick Blotting Paper (C) 

2 Rubber Bands (D) 

1 Jar (E) 

1 Plywood Lid (F) 



Terminals (G) 

Sulphuric Acid (H) 
(Concentrated) 



Dimensions 

80 cm x 7.5 cm x 
0.01 cm 

15 cm x 6 cm x 0.01 cm 

85 cm x 10 cm 



Capacity 1 liter, 
approximately 

10 cm diameter, 
0.5 cm thick 

VIII/A2, Component (4) 

200 ml 



*Adapted from Intermediate Science Curriculum Study, Pr obing the Physical World, 
Volume 1, Experimental Edition, (Tallahassee, Florida: Florida State University, 
1967), pp 1-4. 



b. Construction 
(1) Plates 




Lead (B) 



/ 



(A) 



(B) — 



^aa 





Fold one of the small lead 
sheets (B) down the middle. 
Repeat the process again, but 
this time leave the fold open. 
You now have a tab for attach- 
ment to one of the lead plates. 

Fit the end of one of the 
large lead sheets (A) into one 
of the tabs (B) , and fold the 
tab firmly down over the sheet 
using a pencil to flatten the 
tab down. With the lead sheet 
fully inserted into the tab, 
fold the tab once more, and 
smooth it again. You now have 
one lead plate complete with 
tab. Now make a second lead 
plate complete with tab in an 
identical manner, using the 
remaining lead sheets (A and B) . 

Make a plate "sandwich" by 
placing the blotting paper (C), 
lead plate, blotting paper (C), 
lead plate one on top of the 
other. The tabs should be at 
opposite ends of the sandwich, 
but emerging from the same side. 



Blotting 
Paper (C) 



Lead (A) 



-187- 



Tabs 



Plates 




Rubber 
Bands (D) 



Roll the "sandwich" up into a 
tight cylinder. One tab will 
protrude from the center and 
one from the edge. Hold the 
plates in the form of a cylinder 
by wrapping the rubber bands 
(D) around the cylinder. 



(2) Container 



Tabs 




Terminals (G) 



Lid (F) 




Mpl^ 




Lid (F) 



Plates 



Cross Section 



Obtain a one liter jar (E), 
and use the plywood lid (F) to 
cover the open end of the jar. 
Bore two holes (0.5 cm diameter) 
through the lid to accommodate 
the tabs, one hole being at the 
center of the lid and the other 
2.5 cm away from the first hole. 
Drill two more holes (0.3 cm 
diameter) , one on either side 
of the first two holes to 
accommodate the terminals. 
Drill a fifth hole (1 cm dia- 
meter) anywhere else in the lid 
to permit addition of the 
electrolyte. 

Push the plate tabs through the 
two larger holes in the lid 
(the center tab through the 
center hole) , and fold the top 
1.5 cm of each tab over at right 
angles so that each overlaps the 
adjacent small hole in the lid. 
Fit two terminals (G) into the 
small holes in the lid, and 
lock a tab under each terminal. 
Make one liter of electrolyte 
in a separate container. This 
may be dilute sulphuric acid 
or sodium sulphate. Sulphuric 




Level of 
Electrolyte 



acid is the better electrolyte, 
but from a student point of 
view it can be dangerous if it 
is not handled carefully. Many 
will prefer to use sodium 
sulphate for this reason. 

To make the sulphuric acid 
electrolyte pour 813 ml of water 
into a container. Then add 187 
ml of concentrated sulphuric 
acid (H) to the water in very 
small quantities , letting the 
acid run down the sides of the 
container into the water. Much 
heat will be caused by the inter- 
action. Stir the electrolyte, 
and allow it to cool before 
adding more concentrated acid. 
Before pouring the electrolyte 
into the battery it must be 
completely cool. (If a sodium 
sulphate electrolyte is pre- 
ferred add 1.0 liter of water to 
114 g of solid sodium sulphate 
and stir. ) 

Pour the electrolyte carefully 
through the appropriate hole in 
the lid until it just covers the 
plates. The battery is now 
ready for charging and use. 



110 

AC 



c. Notes 

(i) To charge the battery a DC current of one amp at approximately 2.5 to 3.0 

volts is required. This is best obtained with the help of a transformer (VII/A3) 

and rectifier (VI I /B2 )Gonnect 
the rectifier to the 10 volt taps 
on the transformer, and connect 
the battery across the rectifier 
as illustrated. A variable 
resistor (VIII/C2) should be 
connected into the circuit to 
control the current, and an 
ammeter and voltmeter connected 
as indicated to monitor the 
circuit . 

Charge the battery for 30 minutes 
keeping the current-steady at 
one amp by adjusting the 
variable resistance . (The volt- 
age will not remain constant throughout charge.) 

(ii) Some idea of the strength of the battery may be obtained by discharging it 
through a five ohm resistor, and noting the current generated over a period of 
time, and the voltage of the battery output. The results of one such discharge are 
given below (for the battery with sulphuric acid electrolyte) . 




Battery 
Under Charge 





^ 


1 1 


^ 


























vwwv 

5 -n- 



<2> 



t 

Minutes 


V 

Volts 


I 
Amps 


1 


1.00 


0.40 


__2 


0.40 


0.20 


3 


0.20 


0.10 


4 


0.19 


0.04 


5 


0.19 


0.04 



^ 



Battery 



The voltage and current output fall off rapidly with time, indicating that the 
battery in its present state is not suitable for quantitative experimentation. 

(iii) A good, strong battery may be produced simply by recharging the battery 
and discharging it several times over. This process is more successful if the 
direction of the current is changed for each recharge. The battery tested above 
was charged four more times (each time with reversed polarity) and discharged for 
five minutes through the five ohm resistor after each charge. After each discharge 

the battery terminals were 
shorted to remove any remaining 
charge. The results of the 
fifth discharge show that the 
battery, after repeated charging 
and discharging* is capable of 
maintaining a steady current 
output at a steady voltage, and 
as such is suitable for 
quantitative experimentation. 

(iv) Some idea of the strength of the battery is obtained by comparing the dis- 
charge of a small dry cell (through a five ohm resistor) with the above observa- 
tions. The results indicate that the dry cell is not as steady a source of current 

and voltage as the battery after 
successive recharging, but that 
it is much steadier than the 
battery after only one charge. 



t 

Minutes 


V 
Volts 


I 
Amps 




1 


1.9 


0.39 




2 


1.9 


0.39 




3 


1.9 


0.39 




4 


1.9 


. 


3 


5 


1.8 


0.35 





t 
Minutes 


V 

Volts 


I 
Amps 


1 


1.39 


0.25 


2 


1.37 


0.25 


3 


1.36 


0.24 


4 


1.35 


0.24 


5 


1.35 


0.24 



(v) Somewhat similar results are obtained if the battery is filled with sodium 
sulphate electrolyte and tested in the same way. 



Bl. Bulb Holder with Bulb 



CIRCUIT COMPONENTS 




(3) Terminal 



(2) Holder 



0) Base 



a. Materials Required 
Components 

(1) Base 

(2) Bulb Holder 



(3) Terminals 



b. Construction 



(1) Base 



(2) Bulb Holder 



Qu I tems Required 

1 Wood (A) 



: 



Bulb Holder (B) 



1 Bulb (C) 

2 Brass Bolts (D) 

4 Nuts (E) 

2 Magnet Wire (F) 



Dimensions 
7cmx3cmxlcm 

To hold flashlight 
bulbs 

1.1, 2.5, or 6.2 volts 

0.3 cm diameter, 
2.5 cm long 

0.3 cm internal 
diameter 

4 cm long 



Use the wood (A) to serve as 
the base of the bulb holder. 

Obtain a bulb holder (B) (porce- 
lain or metal) from the local 
market, and screw it onto the 
base. The holder should take a 



-192- 



(3) Terminals 



variety of local bulbs (C) 
(e.g., 1.1 volts, 2.5 volts and 
6.2 volts) . 

Make the terminals from the 
nuts (E) and bolts (D) as 
described in item VIII/A2, 
Component (4) . Use the magnet 
wire (F) to connect the bulb 
and terminals, not forgetting 
to clean the ends of the wire. 



c. Notes 

(i) Bulbs may be used not only to investigate electrical phenomena in simple 
circuits, but also to serve as suitable resistances. 



-193- 



B2. Switch 



© 



(1) Base 




(4) Spring 



(3) Contact Point 



(2) Terminals 



a. Materials Required 
Components 

(1) Base 

(2) Terminals 



(3) Contact Point 



(4) Spring 



b. Construction 



(1) Base 



(2) Terminals 



q u Items Required 

1 Wood (A) 

2 Brass Bolts (B) 
4 Nuts (C) 

1 Brass Screw (D) 

1 Magnet Wire (E) 

1 Brass Sheet (F) 

1 Wooden Dowel (G) 



Dimensions 
7cmx3cmxlcm 

0.3 cm diameter, 
2.5 cm long 

0.3 cm internal 
diameter 

0.8 cm long 
#22, 3 cm long 

5 cm x 1 cm x 0.1 cm 

1 cm diameter, 
0.5 cm long 



Use the wood (A) to serve as the 
base of the switch. 

Make the terminals from the 
nuts (C) and bolts (B) as 
described in item VIII/A2, 
Component (4) . 



©From Reginald F. Melton, E lementary, Economic Experiments in Physics, Apparatus 
(guide, n don: Center for Educational Development Overseas, 1972), pp 129-130. 



-194- 



(3) Contact Point 




Top View 



Screw the brass screw (D) into 
the wood (2 cm from one terminal) 
and connect it to the terminal 
by means of the short length of 
copper wire (E) . 



(4) Spring 



Wood (G) 






rass (F) 



hH 




Make the spring out of the 
piece of brass sheeting (F) . 
Drill a small hole (0.3 cm 
diameter) in one end of the 
spring so that the terminal 
bolt will pass through it, and 
hold the spring in position by 
fastening the terminal locking 
nut. Cut the wooden head (G) 
and attach it to the free end 
of the spring with epoxy resin. 



Side View 



-195- 



63. Circuit Board 



(2) Cell Holder 



(1) Base 



(3) Terminal 




(4) Circuit 
Connectors 



Bulb Holder 



a. Materials Required 
Components 
(1 Base 

(2) Cell Holder 



(3) Terminals 



(4) Circuit 
Connectors 



g u Items Required 

1 Plywood (A) 

2 Wood (B) 

2 Wood (C) 

3 Dry Cells (D) 

2 Metal Strips (E) 

2 Metal Strips (F) 

4 Bolts (G) 

4 Nuts (H) 

8 Washers (I) 

12 Bolts (J) 

12 Nuts (K) 

24 Washers (L) 

12 Coat Hanqer Wire (M) 

10 Metal Strips (N) 



Dimensions 

33 cm x 30 cm x 0.6 cm 

33 cm x 2 cm x 0.5 cm 

30 cm x 2 cm x 2 cm 

1.5 volts each 

4 cm x 2 cm x 0.02 cm 

6 cm x 2 cm x 0.02 cm 

0.3 cm diameter, 
4 cm lonq 

0.3 cm internal 
diameter 

Approximately 1.2 cm 
external diameter 

0.3 cm diameter, 
4 cm lonq 

0.3 cm internal 
diameter 

Approximately 1.2 cm 
external diameter 

10 cm long 

6 cm x 1.5 cm x 0.02 cm 



Copper Wires (0) 



#18, 25 cm long 



Bulb Holders 



b. Construction 
(1) Base 



3 Wood (P) 

3 Coat Hanger Wires (Q) 

3 Eye Screws (R) 

6 Screws (S) 

3 Washers (T) 

3 Metal Sheets (U) 

Assorted Flashlight 

Bulbs (V) 



5cmx3cmx2 cm 

6 cm long 

Approximately 3 cm 
long 

1 cm long, approxi- 
mately 

3 cm x 2 cm x . 02 cm 




Drill 12 holes (diameter 0.3 cm) 
through the plywood (A) in the 
positions indicated. Ifa 
piece of scrap wood is placed 
beneath the plywood during 
drilling the bottom edges of 
the hole will not splinter so 
readily. 

Glue the two strips of wood (B) 
along the bottom edges of the 
base, at right angles to the 
grain of the wood, so that 
bending or warping of the base 
is prevented. 



Botton View 



-197- 



(2) Cell Holder 



3 



t 



0.8 



Wood (C) 



l-^-H 






c 


1 

1 




*~ 1 


.6-f. 


-H 




End Contact 



Use two pieces of wood (C) to 
serve as the cell holder strips. 
Using nails and glue attach 
one strip to the end of the base 
which has not yet been drilled 
with holes. Place the second 
strip parallel to, and about 
3 cm away from, the first strip. 
Adjust the separation between 
the two strips so that they will 
hold three dry cells (D) snugly 
in position. Then glue and nail 
the second strip firmly in 
position. 

Drill four holes (diameter 0.3 
cm) between the two strips as 
illustrated. 

The two strips of flexible 
metal (E) may be cut from a tin 
can (or similar source) . Drill 
a hole (0.3 cm diameter) in the 
end of each sheet, and then bend 
the sheet into the shape of an 
end contact, as indicated. Use 
sandpaper to remove any coating 
which might interfere with good 
electrical contact. 



o 



|— 1.8 -f- 1 .6— (*- 1 .8 —| 




4 C e. n t e r 
Contact 



Two more metal strips (F) may 
be cut from the same source as 
before. Drill a hole (0.3 cm 
diameter) at the mid-point of 
each strip, and then bend each, 
as indicated, into the shape of 
a center contact. Use sand- 
paper to remove any coating which 
might interfere with good 
electrical contact. 



Bolt (G) 
Contact 



Base 




T= ^7 = ^ 



Side View 
(Cross-section) 



Nut (H) 
Washer (I) 

- Washer (I) 



Mount the contacts in position 
on the circuit board base, in 
each instance using a bolt (G) , 
a nut (H) and two washers (I) . 
The purpose of the washers is 
to hold the bolts (which also 
serve as terminals) rigidly in 
a vertical position. 



Cell 



IjJ cen L 



Cell 



-w 



Side View 



(3) Terminals 



Fit 12 terminals in the remain- 
ing holes in the base. Each 
terminal is made in the same way 
as described above, each con- 
sisting of a bolt (J), a nut (K) 
and two washers (L) . 



-199- 



(4) Circuit Connectors 





End 
Loop 



0.4 

H 1 ^ 



Spring 
Catch 




Nail 



Groove 




Solder 



Wire (0) 



^3- 
\ 



Remove any paint or coating 
from the wires (M) with sand- 
paper. Bend one end of each 
wire into a loop, and slip this 
onto one of the terminals. Bend 
the free end of the wire around 
an adjacent terminal so as to 
form a spring catch. Make a 
small lip on the end of the 
catch, thus permitting the 
catch to be readily attached to, 
or released from, an adjoining 
terminal . 

The ten strips of metal (N) 
may be cut from a tin can or 
similar source (brass sheet, 
etc.) . Clean the surfaces with 
sandpaper. Bend each sheet into 
a "U" shape in which the sides 
are 0.4 cm apart. Then place 
a nail (0.2 cm diameter) between 
the sides of the "U" sheet, and 
squeeze the sheet on either 
side of the nail with pliers to 
form a small groove. Make small 
lips on the open ends of the 
"U" sheet to permit easy attach- 
ment to the terminal posts. 
Finally, attach each end of each 
copper wire (0) to one of the 
newly created clips with the 
help of solder. You should now 
have twelve coat hanger wire 
connections and five copper wire 
connections for completing 
circuits . 



Cli P 



Wire (0) Clip 



(5) Bulb Holders 



1.1 



H'h- 



1 

T 



a . 3 



Drill a vertical hole (1.0 cm 
diameter, loti deep) into the 
middle of the top surface of 
the wood(P). Drill a horizont; 
hole (0.3 cm diameter) into the 
middle of one end of the block, 
so as to meet the first hole. 



Side View 



Eyed 

Screw (R) 



Screw (S) 




Wire (Q) 






Loop 



1> 



Spring 

Catch 



Clean the surface of the wire 
(Q) with sandpaper. Insert one 
end of the wire fully into the 
horizontal hole, and using a 
pair of dog-nosed pliers 
(inserted through the vertical 
hole) bend a loop into the 
inserted end of the wire. Insert 
a small screw (S) through the 

loop to attach the wire perma- 
nently within the block. 



Cross Section 



Fit an eye screw (R) into the 
middle of the other end of the 
block, and finally make a spring 
catch in the free end of the 
coat hanger wire (Q) (in just 
the same way as for the circuit 
connectors) so that the holder 
may be readily connected between 
adjacent terminals on the circuit 
board. 




-I'h 




Screw 

Hole 



Slit 



Washer (T) 



Bulb Hold 




screw (s> Raised 

Edge 



Metal 

Sheet (U) 




Cross Section 



The flexible sheet of metal (U) 
may be cut from a tin can, or 
similar source (thin brass 
sheet) . Drill a bulb hole 
(diameter 0.9 cm) and screw hole 
(diameter 0.3 cm) in the sheet 
as indicated. Make a cut in 
the sheet between one outer edge 
and the bulb hole. Ifone side 
of the slit is raised slightly 
higher than the other, the hole 
will serve as a screw socket 
for a bulb (V) . Use a small 
screw (S) and washer (T) to 
attach the metal sheet to the 
top of the block so that the 
bulb hole in the sheet sits 
over the hole in the block. 

The screw (S) should also be 
centered on the block so that 
it makes contact with the 
threads of the eye screw (R) . 
(If this adjustment is found 
difficult, contact between the 

two screws may be made by 
soldering a short length of 

copper wire from one screw to 
the other.) 

Three identical bulb holders 
should be made, each with a 
selection of bulbs (V) (e.g., 
1.1 volts, 2.5 volts, 6.2 volts). 



C. Notes 

(i) The Circuit Board is a very convenient way of setting up electrical circuits. 
A typical series of experiments using such a circuit board will be found in 
Nuffield Foundation, Nuffield Physics, Guide to Experiments 2, (London: Longmdns/ 
Penguin Books, 1967), pp 16-63. 



•OJC- 



C. RESISTORS 



CI. Variable Resistor (Carbon) 



(2) Pencil 
Resistor 



(1) Base 



4) Wires 




a. Materials Required 

Components 

(1) Base 

(2) Pencil 

(3) Clips 

(4) Wires 

b. Construction 

(1) Base 

(2) Pencil Resistor 



(3) Clips 



Qu I tems Required 
1 Wood (A) 

1 Pencil (B) 



2 "U" Tacks (C) 

2 Copper Wires (Cotton or 
Plastic Covered) (D) 



Dimensions 



20 cm x 3 cm x 1 cm 

20 cm long, 
approximately 



#22, 30 cm long 



Use wood (A) as the base. 

Split a soft lead pencil in 
half so that the lead (B) 
protrudes along its axis. It 
is important that the lead 
should not be broken or cracked 
by this process. 

Take two U-shaped tacks (C) s 
normally used for securing 
electrical leads, and secure 
the pencil (B) to the base (A) . 
One of the clips should be left 
relatively loose. 



(4) Wires 



;mi r 



Cross Section 



Take the bare end of a length 
of copper wire (D), and wrap it 
around the loose clip, so that 
when the latter is tapped 
securely into position the 
copper wire makes good contact 
with the pencil lead. 



C. Notes 



a z? 



U 



Resistor 



I ft he resistor is connected into a circuit in series with two dry cells 
1 (1.5 volts each) and a flash- 

light bulb (approximately 1.5 
volts), it will be found that 
increasing the length of pencil 
lead included in the circuit 
will diminish the brightness of 
the bulb, the full length of 
lead (approximately 20 cm of 
#2B lead) almost extinguishing 
the light altogether. 

Dry Cells 




Bulb 



C2 . Variable Resistor (NichfOHie) 



-204- 



(3) Sliding 
Contact 




(4) Terminals 



(1) Resistance Coil 



(2) Coil Support 



a. Materials Required 
Components 
(1) Resistance Coil 



(2) Coil Support 



(3) Sliding Contact 1 



Qu Items Required 
1 Wooden Dowel (A) 

1 Asbestos Paper (B) 
1 Nichrome Wire (C) 

1 Wood (D) 

2 Wood (E) 

2 Plywood (F) 

Wood Dowel (G) 
Wood Dowel (H) 



1 


Brass Strip (I) 


1 


Bolt (J) 


3 


Nuts (K) 




Washers (L) 



Dimensions 

2 6 cm long, 2.5 cm 
diameter 

40 cm x 2 6 cm 

#20, 450 cm long 

30 cm x 7.5 cm x 2 cm 
8 cm x 7 . 5 cm x 2 cm 
30 cm x 3 cm x 0.7 cm 

3 cm diameter, 3 cm 
long 

3 cm diameter, 1 cm 
long 

13 cm x 1 cm x 0.02 cm 

0.3 cm diameter, 6 cm 
long 

0.3 cm internal 
diameter 

1 . 2 cm external 
diameter 



(4) Terminals 



2 Bolts (M) 



4 Nuts (N) 



. 3 cm diameter, 2.5 
cm long 

0.3 cm internal 
diameter 



b. Construction 



(1) Resistance Coil 




Wooden 
Dowel (A) 



Asbestos 
Paper (B) 




Nichrome 
Wire (C) 



The dimensions of the apparatus 
depend very much on the resis- 
tance required. In this case 
a 25 ohm resistor, capable of 
carrying a current of up to 
3 amps was required, and it was 
decided that this could be 
achieved by using some 400 cm 
of #20 nichrome wire which had 
a resistance of approximately 
1 ohm per 16 cm length. This 
determined the dimensions of the 
coil and the resulting item of 
equipment . 

Attach the asbestos paper (B) to 
the wooden dowel (A) , as indi- 
cated, with two or three short 
nails, and then wrap the paper 
closely around the dowel. There 
should be enough paper to make 
about five layers. Attach the 
loose end of the asbestos paper 
to the dowel with two or three 
more short nails. 

Attach the nichrome wire (C) to 

one end of the dowel by means of 

a nail, leaving about 7 cm of 

wire as a free end. Wrap the 

wire firmly around the dowel to 

make a coil with a regular 0.5 

cm between turns. Do not allow 

the wire to touch any of the 

nail heads in the dowel, thus 

avoiding a "short" between 

adjacent turns. On reaching the 



-206- 



(2) Coil Support 




end of the dowel, attach the 
wire once more to the dowel 
with a short nail. Cut off any 
unnecessary wire, leaving about 
7 cm as a free end. 

Make a support for the resistance 
coil from wood (D) for the base 
and wood (E) for the two Si de- 
pieces . Nail the resistance 
coil between the sidepieces (E) 
such that it is 2 cm from the 
top of, and on the median 
bisecting, each sidepiece. 



Sidepiece (E) 



Side View 



Sidepiece (E) 



Top Pieces (F) 



Set the two pieces of ply- 
wood (F) in position on top 
of the support as indicated, 
but only screw one piece in 
position for the moment. 



Top View 



(3) Sliding Contact 




Dowels 



1.5. 



T 



Bore a hole (diameter 0.3 cm) 
along the axis of each dowel 
(G,H). Similarly, drill a ho 
(0.3 cm diameter) at a distance 
of 1.5 cm from either end of 
the brass strip (I) . 



Brass Strip (I) 



Nuts (K) 



Washers (L) 
Dowel (H) 




Bolt (J) 



Dowel (G) 



Nut (K) 



Brass 
Strip (I) 



Side View 
(Cross-section) 



Bolt (J) 




Nuts (K) 

Dowel (G) 
Washers (L) 



Top Pieces (F) 
Dowel (H) 
Brass (I) 

Asbestos (B) 
Dowel (A) 



Sidepiece (E) 



V///////////////A — °- (0, 



Bend the brass strip (I) into a 
semicircular shape around the 
smaller dowel. Insert the bolt 
(J) through the lower dowel (H) 
and the end holes in the brass 
strip (I). Lock the strip in 
position with a nut (K) , and 
then add washers (L) (no more 
than 1.2 cm in diameter) to 
create a spacer between the two 

dowels of 8.8 cm depth, slide 

the larger dowel (G) onto the 
bolt, and fix it in position 
with a locking nut (K) . Add 
another nut (K) to serve as a 
terminal . 

Place the sliding contact above 
the resistance coil so that the 
fixed top piece of the support 
fits into the space between the 
dowels of the sliding contact. 
Take the second top piece (F) 
already cut, and set it in 
position on top of the support 
so that it holds the sliding 
contact in position in contact 
with the resistance coil. Screw 
the top piece in position on 
top of the endpieces. If neces- 
sary, adjust the position of the 
resistance coil to insure not 
only that there is good electri- 
cal contact between the sliding 
contact and the resistance coil, 
but also that the contact slides 
smoothly along the length of 
the coil. 



End View 
(Cross-section) 



(4) Terminals 



Sliding. 
Contact' 



Terminal 

l 

A 



wmi iiiiiiiiiiiiiiiiiiiiiiiii/iiiih 



s 



I 



Top Piece (F) 



Resistance 

Coil 



Use the nuts (N) and bolts (M) 
to make two terminals [see 
VIII/AZ, Component (4)], one at 
either end of the support top 
piece, and fasten the free ends 
of the resistance coil to these 
terminals . 



Side View 



C. Notes 

(i) If the resistor is connected into a circuit by means of the two fixed 
terminals, a fixed resistance of 25 ohms is added to the circuit. If the terminals 
used are one fixed terminal and the terminal on the sliding contact, then the 
resistance added to the circuit may be varied from 25 ohms to almost zero. 

(ii) A current passing through the coil will tend to heat it up. A Z-amp 
current makes the coil fairly hot, and a 3-flUip current makes it very hot, but the 
heating does not affect the performance of the resistor. 



C3. Decade Resistor 



zuy- 




(1) Base 



(3) Resistors 



(4) Connectors 



(2) Terminals 



a. Materials Required 
Components 

(1) Base 

(2) Terminals 



(3) Resistors 



(4) Connectors 



b. Construction 



(1) Base 



Qli Items Required 
1 Wood (A) 

5 Bolts (B) 
10 Nuts (C) 

Washers (D) 

Resistor (E) 
Resistor (F) 
Resistors (G) 
Copper Wire (H) 
Screws (I) 

Brass Strips (J) 



20 
1 

















3 


o o— c 


) O < 




1 


















2 




- 5 -J 


- 5 - 


- 5 — 1 


- 5 - 


2.5 


♦ 



Dimensions 

2 5 cm x 7 cm x 2 cm 

0.4 cm diameter, 5 cm 
long 

0.4 cm internal 
diameter 



10 ohms, 2.5 watts 
20 ohms, 1.5 watts 
30 ohms, 1 . watt 
#24 , 30 cm long 
1.5 cm long 

7.5 cm x 1.5 cm x 
0.05 cm 



Use wood (A) for the base. Mark 
on the top surface the position 
of the terminals and screws as 
indicated. 



iTerminal Positions 
Screw Positions 



(2) Terminals 



Bolt (B) 
Washer (D) 




Nuts (C) 



Base (A) 



'Washer (D) 



Drill holes (0.4 cm diameter) 
in the base (A) in the terminal 
positions, making sure that the 
holes are at right angles to the 
plane of the base. Use a bolt 
(B), two nuts (C) , and two 
washers (D) to make each ter- 
minal . 



(3) Resistors 




Top View 



Insert five screws (I) into the 
base in the positions indicated. 
Connect each screw to the neares" 
terminal with a short length of 
copper wire (H) . Connect radio 
resistors (E, F, G) (see notes) 
of 10, 20, 30 and 30 ohms betwee: 
successive pairs of screws (see 
notes) . 



(4) Connectors 



^k 



1.0 




Connector 



Terminal 



Make four connectors from the 
brass sheeting (J) . Drill a 
hole (0.7 cm diameter) at a 
distance of 1.0 cm from each 
end. Squeezed gently into the 
shape of an arc, it should be 
possible to set the connector 
across two terminals, thus 
shorting one of the resistors 
out of the circuit. 



Side View 



-211- 



c. Note s 

(i) The resistance between the main terminals (T) may be any multiple of 10 
ohms from to 90, according to the way in which the connectors are placed across 

the terminals. In the case 

T T 

illustrated the resistance 
would be 50 ohms . 



^1 




— A> — CD *- 



-m — 1> 



10 



20 



3C 



30 



(ii) If the decade resistor is designed for use with a voltage supply of no 
more than 5 volts then the 10, 20, and 30 ohm resistors purchased should have 
ratings of 2.5, 1.5 and 1.0 watts respectively. 



R 
Ohms 


V 
Volts 


I 
Amps 


W 

Watts 


10 


5 


0.50 


2.50 


20 


5 


0.25 


1.25 


30 


5 


0.17 


0.83 



Alternatively, if all the resistors purchased were rated at 1 watt, then 
the voltage placed across the 10, 20 and 30 ohm resistors should never exceed 
3.0, 4.5 and 5.5 volts respectively. 



R 
Ohms 


W 

Watts 


V = W.R 

Volts 


10 


1.0 


3.2 


20 


1.0 


4.5 


30 


1.0 


5.5 


40 


1.0 


6.3 


50 


1.0 


7.1 


60 


1.0 


7.6 


70 


1.0 


8.4 


80 


1.0 


8.9 


90 


1.0 


9.5 



Dl. Simple Motor 



(2) Rectangular 
Coil 



-ziz- 



D. DYNAMO /MOTORS 




(3) Electromagnet 



(1) Base 



a. Materials Required 
Components 
(1) Base 



(2) Rectangular 
Coil 



(3) Electromagnet 



Qtl Items Required 

1 Wood (A) 

4 Bolts (B) 

a Nuts (C) 

2 Coat Hanger Wire (D) 

1 Roll of Magnet Wire (E) 

1 Coat Hanger Wire (F) 

1 Insulating Tape (G) 

1 Masking Tape (H) 

2 Magnet Wire (I) 
4 Thumbtacks (J) 

1 Soft Iron Bar (K) 

1 Roll of Magnet Wire (L) 

1 Masking Tape (M) 

2 Wood Strips (N) 



Dimensions 

14 cm x 13 cm x 1.5 cm 

0.3 cm diameter, 
3.0 cm long 

0.3 cm internal 
diameter 

7 cm long, 0.2 cm 
diameter 

#26 

10 cm long, 0.2 cm 
diameter 



#26, 10 cm long 



17.5 cm x 2.0 cm x 
0.3 cm 

#26, approximately 
100 g 



a cm x 1 . 5 cm x 1 . cm 



b. Construction 



(1) Base 





1 


2 

-i 


~\ 


(51 


' 1.5 

Base (A) 


l 
si— 


1 


® 


3.5 


m 






■ 14 







Use wood (A) as the base. Use 
the four bolts (B) and eight 
nuts (C) to make four terminals 
[see VIII/A2, Component (4)]. 
Attach a terminal at each corner 
of the base, making sure to 
inset the boltheads into the 
bottom of the base. Drill two 
holes (0.2 cm diameter, 1.0 cm 
deep) into the base to hold the 
vertical supports. 



Top View 



0.3 



Wire (D) 



Make two vertical supports for 
the coil by twisting the coat 
hanger wire (D) into the shape 
indicated. Set the supports 
vertically upright in the newly 
drilled holes in the base. 



(2) Rectangular Coil 



Cardboard Form 
I 




Wind 30 turns of magnet wire 
(E) around a cardboard form in 
order to make a coil of internal 
size 3.5 cm x 1.5 cm. Leave 
10 cm of wire free at either 
end of the coil. 



-214- 



Axle (F) 




Take the length of straight 
coat hanger wire (F) and thread 
it through the middle of the 
coil to serve as the axle. W r a 
the masking tape (H) around the 
coil and axle to hold the coil 
firmly in position. 




Axle (F) 



Coil 



Tape (H) 



Tape (H) 
Tape (G) 



Ends of Coil 

Wire 



Wrap a length of insulating 
tape (G) around the axle, adja- 
cent and external to the coil, 
to create a region of insulation, 
1.5 cm long, on the axle (F) . 

Adjust the ends of the coil 
wire so that they lie parallel 
to this insulated portion of the 
axle, and on either side of it. 
Cut the parallel wires so that 
they do not protrude beyond the 
insulation. Clean the enamel off 
the wire with sandpaper. 




Terminal 



Thumbtacks (J) 



Fasten a thin piece of masking 
tape (H) around the ends of the 
coil wire and axle, thus keeping 
the ends of the coil wire in 
position. Fit the coil axle 
into the coil supports on the 
base. Take the two lengths of 
copper wire (I), and remove the 
varnish from the ends. Make one 
end of each wire into a vertical 
contact which just touches one 
of the wire ends from the coil. 
Hold each wire in position on 
the base with thumbtacks (J), 



-215- 



(3) Electromagnet 



con — : 4 



f 



1.0 






i, 



Tzz. 



J 



— Coil 



Connecting Turns 



and attach the free end of the 
wire to one of the front termi- 
nals as indicated. 

A simple horseshoe magnet, with 
poles about 4 cm apart, will 
serve the purpose well. How- 
ever, if a suitable horseshoe 
magnet is not available, an 
electromagnet may readily be 
made as follows. 

Take a soft iron bar (K) , and 
bend it into a horseshoe shape 
with parallel sides 4 . 5 cm 
apart. Take about 100 g of 
#26 magnet wire (L) , and wind a 
coil on each side of the U- 
shaped bar. Each coil should 
be about 4 cm long, and should 
contain ten layers of wire. The 
coils should be connected in 
series to one another, simply 
by continuing the windings in 
the same direction around the 
bar from one coil to the other 
in a series of widely spaced 
connecting turns. Cover the 
final layer of turns with 
masking tape (M) to hold the 
coils in position. Connect the 
free ends of the coils to the 
rear terminals on the base. 

Place two wood strips (N) 
beneath the electromagnet such 
that the magnetic poles are 
either side of, and at the same 
height as, the middle of the 
rectangular coil. 



-216- 



c. Notes 

(i) With a current of 1 amp through the electromagnet and about 0.7 amp through 
the rectangular coil, the latter will rotate quite rapidly, thus behaving as a 
motor. The current required may be readily provided by dry cells. 

(ii) With a current of 1 amp through the electromagnet it is possibll to generate 
a current in the rectangular coil by rotating it as rapidly as possible. However, 
the current generated is extremely small (of the order 0.1 milliamps) . . 



D2 . Dynamo/Motor 



© 



(6) Terminals and 
Electrical Wiring 



(7) Driving Wheel 



(5) Commutator 




(l)Base 



(2) Armature 



(4) Axle Supports 



(3) Pole Heads 



a. Materials Required 
Components 

(1) Base 

(2) Armature 



(3) Pole Heads 



Qu Items Required 

1 Wood (A) 



1 


Nail (B) 




1 
1 


Box of Nails (C) 
Epoxy Resin (D) 




1 


Roll of Magnet Wire 


(E) 


: 


Box of Nails (F) 




: 


Epoxy Resin (G) 




4 


High Quality Steel 





Dimensions 



2D cm 


x 15 


cm x 


0.7 cm 


diameter, 


15 cm 


long 




4 cm 1 


ong 




#26 






4 cm 1 


ong 





7 cm x 1 cm x 1 cm 



(C) From Reginald F. Melton, El ementary, Economic Experiments in Physics, Apparatus 
(£uILde,n don: Center for Educational Development Overseas, 1972), pp 61-/3 



(4) Axle Supports 



(5) Commutators 



Terminals and 
Electric Wiring 



(7) Driving Wheel 
System 



2 Brass Sheets (I) 

1 Masking Tape (J) 

1 Brass Tube (K) 

1 Epoxy Resin (L) 

2 Brass Sheets (M) 

1 Brass Tube (N) 

2 Brass Sheets (0) 
1 Magnet Wire (P) 

4 Bolts (Q) 

a Nuts (R) 

1 Magnet Wire (S) 

1 Wooden Spool (T) 

1 Rubber Strip (U) 

1 Wood (V) 

1 Wood Disc (W) 

1 Nail (Y) 

1 Wooden Spool (Z) 

1 Screw (AA) 

4 Washers (BB) 



5.5 cmx 2.0 cmx 0.2 cm 



1 cm long, 1 cm external 
diameter, 0.8 cm 
internal diameter 



5.0 cm x 1.0 cm x 
0.1 cm 

1 cm long, 1 cm external 
diameter, 0.8 cm 
internal diameter 

5.0 cm x 1.0 cm x 0.1 cm 

#26, 15 cm long 

0.3 cm diameter, 
3.5 cm long 

0.3 cm internal diameter 

#26, 40 cm long 

2.5 cm long, 3 cm 
diameter 

9.5 cm x 2.5 cm 

12 cm x 5 cm x 4 cm 

15 cm diameter, 
1.5 cm thick 

0.7 cm diameter, 
6 cm long 

2 . 5 cm long, 2 . 5 cm 
diameter 

4 cm long 

0.8 cm internal diameter 
diameter, approximately 



-219- 



b. Construction 
(1) Base 

(2) Armature 



Axle (B) 



r^ 




Use the wood (A) as the base. 

Take a wooden block, and drill 
a vertical hole (0.8 cm diameter) 
through its center so that it 
can support steel axle (B) . The 
latter may be a very long nail 
with the head removed. 



T 

4 



D 

a 
□ 

D 



13 




Take a sheet of aluminum (13 cm 
x 4 cm) and with the help of an 
appropriate series of end projec- 
tions and holes make it into a 
cylindrical container (4 cm tall, 
4 cm diameter) . 




Wooden Rods 

Top View 



Axle (B) 



Aluminum 
Container 




Place the container on the 
wooden block so that it 
encircles the axle. Take 
two wooden rods (4 cm x 2 cm 
x 1.2 cm) and stand these 
against opposite walls of 
the container. Now fill the 
remaining space in the 
container with the nails (C) 
(or similar soft iron material) 
packed closely side by side 
and parallel to the axle. 



-220- 




(3) Pole Heads 



Armature 

Core 




Armature 
Coil 




Aluminum 
/ Containers 



Wooden 
Rods 



Top View 



Cover the ends of the nails 
(not the wood) at both ends 
of the container with epoxy 
resin (D) , so that when it dries 
the nails are welded together 
into a solid soft iron core, 
penetrated along its axis 
by the steel axle (B) protruding 
4 cm at one end and 7 cm at 
the other. Remove the 
aluminum container and the 
wooden rods. You now have 
the core of your armature. 

Wind as much magnet wire (E) as 
possible into a coil around 
the core, making sure that 
you have about 10 cm of both 
ends left free on completion of 
the coil. Temporarily twist 
the loose ends around the long 
end of the axle. The 
resistance of the coil will 
be approximately 5 ohms. 

The pole heads are made in 
very much the same way as 
the armature core. Two 
open ended aluminum containers 
are reguired this time, one 
cylindrical (5 cm diameter, 
4 cm long) and one a rectangular 
cube (7 cm x 7 cm x 4 cm) . The 
cylindrical one is placed inside 
the rectangular one, and the two 
held apart by two wooden rods 
(2 cm x 1 cm x 4 cm) . Just 
as when making the armature 
core, pack the space between 
the two containers with the 
nails (F) packed parallel to 
the axis of the cylindrical 



-221- 




Aluminum 
Containers 



container. Cover the nail ends 
at both extremities of the 
containers and the wooden rods . 
You will now have two pole heads. 




Pole Heads 







7 




- 5 — 












t 
4 

1 


f 

1 

1 

1 




i 
i 

i 




1 
4 

i 


V 




Polt I ( i 1 i 


•-Be 



Base (A) 



Top View 



Place the pole heads on the 
base in the positions 
illustrated, and attach them 
firmly to the base with the 
help of epoxy resin. 

Complete the system with 
four very strong magnets 
laid parallel to one another 
(North Pole touching North 
Pole) across the gap between 



Magnets (H) 




the pole heads . The magnet may 
be purchased, or made (as 
described under IX/Alfrom 
the steel bars (H) . 



Pole Heads 



(4) Axle Supporters 



Brass (I) 



Q- 



/ 



3.5 



2! 



<=> o xx^ 5 



Make two axle supports out 
of the two brass sheets (I), 
drilling one hole (0.8 cm 
diameter) in the upright 
portion to take the axle, 
and two holes (0.3 cm diameter) 
in the base portion to take 
two screws . 



\ 1 h— 8 ~ 5 — I 

^j _ 



Pole 
Heads 



T[] 



i i 



i i« 



* 



Axle 



V 



Axle Support 
Top View 



Armature 
(Not visible) 



Slide the supports on to 
either side of the axle (B) , 
and attach them firmly to the 
base of the apparatus in the 
position shown. 



-233- 



Pole 
Heads" 



Axle 



Masking 
Tape (J) 

Side View 
(5) Commutators 



Masking 
Tape (J) 



Solder 




Insulation 




Contacts 



The axle may be held firmly 
in position by winding masking 
tape (J) (not scotch tape) 
around the axle next to, and 
just outside, the supports. Do 
this as a last step in construc- 
ting this item, however, 



To make the DC commutator, 

take a piece of brass tubing (K) , 

and cut it to make two halves. 

Take some epoxy resin (L), which 
is a good insulator, and 
coat all the inner surfaces 
of the two halves with resin 
about 0.1 cm thick. 

Rotate the armature coil until 
it is in a vertical plane, 
and then attach the two split 
halves to the axle so that 
the split between the halves 
is in ahorizontal plane . If 
the epoxy resin is thick 
enough, it will not only 
attach the split halves 
firmly to the axle, but will 
also insulate the two halves 
from one another, and from 
the axle itself. 

Take the two loose wires from 
the armature coil and, after 
cleaning the ends with sandpaper, 
solder one to one split half and 
the other to the other split 
half. 




1.0 



0.8 




Cut two identical contacts 
out of the thin brass sheets (M) 
as shown. Attach these to the 
base of the apparatus with 
screws, so that they are in 
spring contact with opposite 
sides of the split halves. 

The DC commutator is now 
complete. 



To make the AC commutator, 
cut two identical rings from 
the brass tubing (N) . 



Rings 



Ring "A" 



Ring "B ,; 




Epoxy 
Resin 



Solder 



Temporarily remove the axle 
support and slide the two 
rings onto the axle. Coat 
a length of axle (0.5 cm long) 
with epoxy resin about . 1 cm 
thick and slide ring "A" into 
position over this. The epoxy 



Contact 




Electrical 
Connections 



resin should be such as to 
insulate the ring from the 
axle as well as to hold it 
firmly in position. 

Ring "B" is soldered to the 
axle about 0.5 cm from ring 
A. Solder insures good 
electrical contact between 
the ring and axle. Two 
contacts, identical to those 
described above, should be 
cut from brass (0), and 
attached to the base so that 
each is in spring contact 
with one of the rings. 

Connect ring "B" electrically 
to one of the split halves 
by soldering a very short 
length of magnet wire (P) from 
ring "B" to the axle and 
another piece from one split 
half to the axle. Don't 
forget to clean the ends of 
the magnet wire with sandpaper 
prior to soldering. 

Connect ring "A" electrically 
to the other split half by 
soldering a length of magnet 
wire (P) from one to the other. 



The AC commutator is now 
complete, 



j) Terminals and Electric Wiring 



Bolt (Q). 



Terminal Nut (R) 

f Locking 
I Nut (R) 



Machined 
Terminal 





Side View 
(Cross-section) 




Fahnstock Clip 





<2 


fe^-J 
















} 


►^ 


N; 



AC 



Drill four holes through the 
base to take four terminals, 
two to serve as an AC outlet 
and two as a DC outlet. 

Make each terminal as described 
under VIII/A2, Component (4) . 
Each terminal requires a bolt 
(Q) , and two nuts (R) . 

It is of course very nice to 
have fairly large nuts which 
can be easily adjusted with 
the fingers. Such nuts are 
probably best made on a 
metal lathe. The nuts might 
both be 1 cm in diameter, with 
the thickness of the terminal 
nut being 0.5 cm and that of 
the locking nut 0.2 cm. 

In some localities it is 
cheaper to purchase terminals 
on the local market. check the 
availability of such items as 
Fahnstock clips which can 
replace the above. Take some 
magnet wire (S), clean the ends 
with sandpaper, and then 
connect the terminals to the 
contacts as illustrated, 
fastening the wire beneath 
the locking nut on the terminal. 



fee 



Top view 



-227- 



(7) Driving Wheel System 



SpOOl (T) 




Rubber 
Covering (U) 



Driving Wheel 
Support 




Top View 



Take the wooden spool (T) and 

fill the central hole with wood 
putty. When the latter is per- 
fectly dry, drill a new hole 
(0.7 cm diameter) along its axis 
so that it will just fit on the 
armature axle. A rubber strip 
(U) may be cut from an old car 
inner tube. Nail it around the 
perimeter of the spool. Tempor- 
arily remove the appropriate 
axle support, and attach the 
spool firmly to the axle with 
epoxy resin. Use wood (V) as a 
support for the driving wheel, 
locating it on the base in the 
position shown. Cut a slight 
inset (0.2 cm) into the base 
to hold the bottom of the support 
(V) firmly, and put some wood 
cement in the inset. Fasten 
the support firmly in position 
with the help of two wood screws 
passing through the base of the 
apparatus . 



Nail (Y) 



Wood 
Disc (W) 




Rubber 
Covering (X) 



Use the wooden disc (W) to serve 
as the driving wheel. The 
rubber strip (X) , cut from an 
old car inner tube, should be 
nailed around the perimeter of 
the disc. Drill a hole (0.8 cm 
diameter) through the center of 
the disc, and pass a nail (Y) 
through it to serve as a pivot. 




Sere 



w (AA) | 

Spool (Z) 



Driving 
Wheel 



Side View 
(Cross-section) 



Washers 



Nail (Y) 



Driving 
Wheel 




Side View 
(Cross-section) 



Drill a hole along the axis of 
the spool (Z) so that the spool 
fits loosely on the screw (AA) , 
but cannot slip over the screw- 
head. Screw the spool onto the 
driving wheel about 4 cm from 
the perimeter. Put washers (BB) 
either side of the spool to 
permit it freedom of motion. 
You now have a handle for the 
driving wheel. 

Washers (BB) should be similarly 
placed on the pivot, either side 
of the driving wheel. 

Finally, hold the driving wheel 
tight against the axle spool, 
and use the pivot (Y) to mark 
the best position to locate it 
permanently in the support. 
This will be at a height of 
approximately 10 cm on the 
support. Drill a horizontal 
hole (diameter 0.7 cm) into the 
support, and fix the pivot 
firmly in the hole with epoxy 
resin. 

Your dynamo/motor is now ready 
for operation. 



C. Notes 

(i) The Dynamo/Motor was tested out with two Nuffield horseshoe magnets 
(Nuffield Physics Item 50/2) across the pole heads; these appear to produce a 
fairly standard field, whereas locally produced ones vary considerably in strength, 
depending on the quality of steel or alnico used. The driving wheel was turned 
at as rapid, but constant, a speed as possible, and was noted to be turned at 



-229- 



4.5 to 5.0 revolutions per second on the average. Under these conditions the 
following observations were made: 

The dynamo was found to produce up to 1.1 volts DC and 1.2 volts AC on open 
circuit . 

Connected in series with a small bulb (1.1 volts, 5 ohms) the dynamo pro- 
duced a DC current of 0.11 amp at 0.25 volts, and an AC current of 0.13 amp at 
0.5 volts. On both occasions the bulb was noted to flicker faintly. 

(ii) With the driving wheel disconnected, it was noted that a voltage of 1.4 
volts, producing 0.2 amp, was capable of driving the motor. 



ix. ELECTROMAGNETISM apparatus 

A. ELECTROMAGNETISMAPPARATUS 

The apparatus in this group is primarily concerned with the creation of magnetic 
fields in various forms. 



-231- 



A. ELECTROMAGNETISMAPPARATUS 



Al, Magnetizing Coil and Magnets 



© 



(4) Coil 




ti\ Endpieces 



(2) spool 



(1) Base 



a. Materials Required 
Components 

(1) Base 

(2) Spool 

(3) Endpieces 

(4) Coil 



Qu I tems Required 

1 Wood (A) 

1 Wooden Dowel (B) 

2 Wooden Strips (C) 

1 Roll of Magnet Wire (D) 

1 Switch (E) 

1 Double Electrical Cord (F) 

1 Two Pin Plug 

1 Insulating Tape (H) 



Dimensions 

15 cm x 15 cm x 2 cm 

3 cm diameter, 
8 cm long 

8 cm x 8 cm x 0.5 cm 

#22, 1 kg 

220 volts 

#20, 200 cm long 

220 volts 



(£) From Reginald F . Melton, E lementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 1972), pp 138-142. 



-151- 



b. Construction 

(1) Base 

(2) Spool 



Dowel (B) 



Axial Hole 




(4) Coil 



/ \ 

Dowel (B) Endpiece (c> 




Soool 
Nail Holes 

Nails 



Use wood (A) as the base. 

Drill a hole (2 cm diameter) 
along the axis of the wooden 
dowel (B) to make an appropriate 
spool. 

Drill a hole (2 cm diameter) 
in the middle of each wood 
strip (C) and attach the strips 
to either end of the spool with 
wood cement. 



Wind all of magnet wire (D) on 
to the spool taking care to 
leave about 25 cm of free wire 
at either end of the coil for 
appropriate connections. The 
winding of the coil may be 
facilitated by the use of a 
brace as follows. 

Hammer two large nails (15 cm 
long) into the side of a bench 
so that they protrude horizon- 
tally some 50 cm apart. Place 
the spool to be wound on one of 
the nails. Fasten the first 
turn of magnet wire around the 
spool in such a way that it 
will not slip on turning the 
spool. Then get your partner 
to hold the wire taut over the 
second nail so that it may be 
wound under tension. 



-lii- 




Endpiece (C) 
Coil (D) 



Loop 




Base Insets 



Attach a short shaft (2 cm long, 
lcm diameter) to the center of 
a circular disc (7 cm diameter, 
0.5 cm thick) by means of a 
screw. Hamner three nails 
through the perimeter of the disc 
and drill three corresponding 
holes in the endpiece of the 
spool to take the protruding 
nails. Clamp the jaws of the 
brace firmly on to the shaft. 
Lock the disc and spool together 
by means of the disc nails, and 
then begin to wind the coil by 
turning the brace. 

Drill a small hole in each 
endpiece and loop the wire ends 
through these holes to prevent 
unwinding of the coil. 



Make two insets (8 cm long, 
0.5 cm wide, 0.2 cm deep) in 
appropriate positions on the 
base to hold the endpieces. 
Fix the endpieces firmly in the 
insets with wood cement. 



Attach switch (E) to the base, 
and connect one of the loose 
wires from the coil to the 
switch. Insert a screw into the 
base as indicated, and attach 
the other wire from the coil. to 
the newly inserted screw. Take 



-234- 




Screw 



Electrical Cord (F) 



Coil 



the double electrical cord (F) 
with two pin plug (G) attached, 
and connect one wire to the 
screw, and the other wire to 
the switch. 

Since the coil and wires will 
carry a high voltage (220 volts), 
it is important that all 
wiring should be covered with 
insulating tape (H) . Cover the 
coil, the wire and the screw 
with the tape. 



c. Notes 

(i) To magnetize an item, place a suitable steel specimen in the center of the 
coil. Switch the current quickly on and off. The specimen will be magnetized on 
removal from the coil. 

Ticonal is an ideal alloy for making magnets, but is rarely available on 
local markets. High quality tool steel is a good second best, and is generally 
found in good quality tools (chisels, screwdrivers, drill bits, etc.), as well as 
domestic items such as razor blades and sewing needles. 

Unfortunately, the "high grade steel' sold on many local markets tends to 
to be of poor quality, and does not retain magnetism well. However, if the steel 
is heated to red heat in any oxy-actylene flame, and then quenched in cold water, 
it tends to be hardened, and hold magnetism somewhat better. (It should be noted 
that "steel rods" used in construction work for reinforcing concrete are made of 
soft iron, and cannot be permanently magnetized. 

This magnetizing coil is designed for use with a 220 volt mains supply, 
and is capable of producing extremely strong magnets, It would also work with a 
110 volt supply, but the magnetism induced in a given specimen would be weaker 
than with a 220 volt supply. The magnetizing coil should never be switched on and 
left on, as it would overheat and burn out. It is designed for usage over very 
short periods of time (2 or 3 seconds only) . 

To demagnetize a specimen, place the magnet inside the coil and hold its 
end very firmly. Switch on the current, and remove the specimen from the coil 
maintaining a firm grip on it. The current is not switched off until the specimen 
is completely out of the coil. 



-235- 



A2 . Multipurpose Coil with Cores 



(1) Coil 




(2) Core 



a. Materials Required 
Components 
(1) Coil 



(2)Core 



o, Construction 



(1) Coil 



q u Items Required 

1 Dowel (A) 

2 Wood Strips (B) 

1 Roll of Magnet Wire (C) 

1 Masking Tape (D) 

2 Brass Bolts (E) 

4 Nuts (F) 

1 Bolt (G) 

1 Soft Iron Plate (H) 



Dimensions 

1.2 cm diameter, 
3 cm long 

3cmx2cmxo . 5an 

#22 

0.3 cm diameter, 
1.5 cm long 

0.3 cm internal diameter 

0.4 cm diameter, 
4.5 cm long 

3 cm x 2 cm x 0.3 cm 



The size of the coil is not 
critical, but it does affect 
the spacing and size of 
components used on the Magnetic 
Field Apparatus (IX/A4) and 
Moving Coil Galvanometer (X/C2) . 



1.0 



Axial 
Hole 



Drill a hole (0.6 cm diameter) 
along the axis of the dowel (A) . 



Dowel (A) 



Endpiece (B) 




Corners 
Removed 



Axial Hole 



Dowel (A) 
Position 



Endpiece (B) 



Drill similar holes in the two 
wood strips (B) , at a distance 
of 1.0 cm from the ends, so that 
when the strips are attached 
to either end of the wooden 
dowel (A) they serve as endpieces 
with a common axial hole, cut 
off the top corners of the end- 
pieces, and smooth them down 
with sandpaper. 



(A)" 




Magnet 
Wire (C) 



Wind ten layers of magnet wire 
(C) on to the dowel, leaving 
about 10 cm of wire free at 
either end of the coil. Cover 
the final layer of wire with 
masking tape (D) to hold the 
coil in position. 



Endpieces (B) 




Terminals 



Use bolts (E) and nuts (F) to 
make two terminals as described 
under VIII/A2, Component (4), 
and attach them to one endpiece 
as indicated. 

Clean the ends of the two wires 
from the coil, and fasten them 
under the locking nuts of the 
respective terminals. Make sure 
that it is possible to see the 



(2) Core 



i::y:v::.: 



\»wJMmmmWMM/W$ ^ •<-- Bo 1 1 (G) 



Inset 



way in which the wire from each 
terminal begins to wind around 
the coil, for this makes it 
possible to determine the 
direction of the current around 
the coil, and hence the direction 
of the magnetic field produced. 

Drill an inset (0.4 cm deep, 
1.0 cm diameter) over the hole 
in the endpiece which contains 
the terminals. Insert bolt (G) 
in that the bolthead sits snugly 
in the inset. 



Bolt (G) 




Drill a hole (0.4 cm diameter) 
through the center of the iron 
plate (H) . Make a thread (0.4 
cm diameter) in the hole, and 
attach the iron plate to the 
bolt (G) by means of the 
threaded hole. 



Plate (H) 



c. Notes 

(i) The multipurpose coil may be used in a wide range of experiments to produce 
magnetic fields. It may also be used in instruments [e.g., the Magnetic Field 
Apparatus (IX/A4) and the Moving Coil Galvanometer (X/C2)] where a fixed magnetic 
field is required. 



-238- 



A3 . Magnetic Field Apparatus 



© 




(1) Support 



(2) Field Syste 



a. Materials Required 
Components 
(1) Support 



q u Items Required 

1 Wood (A) 

1 Wood (B) 

2 Wood Screws (C) 
2 Brass Bolts (D) 

4 Nuts (E) 

1 Bolt (F) 

1 Nut (G) 

2 Thumbtacks (H) 



Dimensions 

10 cm x 7 cm x 1 cm 

10 cm x 4 cm x 2 cm 

2 cm long 

0.3 cm diameter, 
2 cm long 

0.3 cm internal diametei 

0.2 cm diameter, 
2 cm long 

0.2 cm internal diametei 



(C) From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatu s 
Guide, '(London: Center for Educational Development Overseas, 1972), pp 146-148. 



-239- 



(2) Field System 



b. Construction 
(1) Support 



Upright (B 



Adjustment 

Screw (F/G) 



Base (A) 



2 Brass Rods (I) 

2 Nuts (J) 

2 Magnet Wires (K) 

1 Aluminum Rod (L) 

1 Horseshoe Magnet (M) 



0.4 cm diameter, 
5 cm long 

0.3 cm internal 
diameter 

#22, 8 cm long 

0.3 cm diameter, 
4 cm long 




Terminals (D/E) 




Bolt (F; 
Nut (G) 

Base (A) 



Use wood (A) as the base. 

Attach wood (B) vertically to 
the base with two wood screws 
(C) passed through the base (4 
cm from one end) . Use wood 
cement to insure a firm joint 
between the upright and base. 

Use the bolts (D) and nuts (E) 
to make two terminals, as 
described under VIII/A2, Com- 
ponent (4), and attach these to 
the base (A) just behind the 
upright (B) . 

Drill a hole (0.3 cm diameter) 
through the base to take bolt 

(F) . Inset nut (G) over the 
hole by striking it into posi- 
tion with a hammer Thread the 
bolt through the nut thus pro- 
ducing an adjustment screw for 
levelling the base. At opposite 
corners on the other side of 
the base, insert two thumbtacks 

(H) beneath the base, so that 
the latter sits on three points, 
the adjustment screw and two 
thumbtacks . 



-240- 



(2) Field System 



Upright (B) 



Lightweight 
Roller (L 



Brass 

Rods (I) 




Nuts (J) 



Wire (K) 



Terminals (D/E) 



Drill two horizontal holes 
(0.4 cm diameter) through the 
upright (B) . It is important 
that the two holes should be at 
exactly the same height (6 cm) 
above the base, and that they 
should be perfectly horizontal. 

Take the two brass rods (I), and 
thread the end of each (thread 
diameter 0.3 cm). Pass the rods 
through the newly drilled holes, 
and use epoxy resin to hold 
them firmly in position. (Avoid 
getting the resin on the pro- 
truding rod since it is an in- 
sulator) . Attach nuts (J) to 
the rod ends, and connect the 
rods and terminals to one another 
with magnet wire (K) . 

Place rod (L) across the hori- 
zontal brass rods to serve as 
a lightweight roller. 

Purchase a strong horseshoe 
magnet (M) from a local shop. 
It may be held in position by 
hand, thus creating a vertical 
magnetic field at right angles 
to the lightweight roller. 



Notes 



(i) If three dry cells (1.5 volts each) are connected across the terminals, a 
current will pass through the lightweight roller at right angles to the magnetic 
field, and the roller will be propelled along the horizontal rods. This piece of 
apparatus may be used for studying the force exerted on a current carrying 
conductor placed in a magnetic field. 



(ii) Should there be any difficulty in obtaining a strong horseshotaagnet, then 
multipurpose coils may be used to replace the magnet. Such a system is described 
in the next item (IX/A4) . 



-241- 



A4. Magnetic Field Apparatus with Mn 1 t i purpose CflJ-LS. 



(3) Coil Holders 



(2) Multipurpose 



(1) Basic Appa 




erminals 



a. Materials Required 
Components 
(1) Basic Apparatus 



(2) Multipurpose 
Coils 

(3) Coil Holders 



q u Items Required 

1 Magnetic Field 
Apparatus (A) 



2 Multipurpose Coils with 
Cores (B) 

2 Brass Sheets (C) 
4 Screws (D) 

4 Brass Sheets (E) 



Dimensions 

IX/A3, No magnet 
reguired 

IX/A2 



2 cm x 2 cm x 0.02 cm 

Approximately . 6 cm 
long 

3 cm x 0.8 cm x 0.05 cir 



(C) From Reginald F - Melton, Elementary; Economic Experiments in Physics, Apparatuo 
Guide (London: Center for Educational Development Overseas, 1972), pp 149-152. 



-242- 



(4) Terminals 



b. Construction 

(1) Basic Apparatus 



Screws (F) 



2 Brass Bolts (G) 



4 Nuts (H) 



1 Magnet Wire (I) 



(2) Multipurpose Coils 



Dsr^ 



Pole Head 




Approximately . 6 cm 
long 

0.3 cm diameter, 
2 cm long 

0.3 cm internal 
diameter 

#24 

Make the Magnetic Field 
Apparatus (A) as described 
under IX/A3. A horseshoe magnet 
is not required, and the magnetic 
field is produced by means of 
the additional components 
described below. 

Make two Multipurpose Coils (B) , 
complete with pole heads, as 
described under IX/A2 . Cut a 
horizontal groove in the front 
endpiece of each (just beneath 
the pole heads) to insure a 
good grip for the coil holders. 



Groove 



(3) Coil Holders 



Screw 
Holes 




Bend 0.3 0.6/ 0.3 
Lines 

Brass Sheet (C) 




0.3 



Bend the two brass sheets (C) 
into spring holders as indicated. 
Drill two screw holes in the 
center portion. 



Spring Holder 



Slot 



Screw 
Hole 



ftJl 



0.6 



Cut a slot (0.7 cm x 0.3 cm) in 
the end of each of the brass 
sheets (E) and drill a screw 
hole in the other end, thus 
producing four clip holders. 



Clip Holder (E) 



1.0 



in 



1.3 



If) 



Bend Line 



Bent Clip (E) 



Clip Holder (E) 



Spring Holder (C 



Coil Terminals 
/ 




Coil Terminal 



Bent Clip 
Holder (E) 



Upright 



Base 



Bend two of the holders at right 
angles to make L-shaped clips as 
follows . 

Measure the distance from the 
center of the coil terminal to 
the upright. Let's say this is 
1 cm. Then the clips must be 
bent at right angles at 1.3 cm 
from the slotted end. Fit the 
slotted end of each clip holder 
under the locking nut of a ter- 
minal on the lower coil, and use 
screws (F) to attach the clips 
to the upright. 

Use screws (D) to attach the 
spring holders horizontally to 
the upright of the apparatus, 
1 cm above, and 1 cm below, the 
horizontal rods. Clip the 
multipurpose coils temporarily 
in the spring holders, and mark 
out the positions of the free 
endpieces of the coils. 

Cut the top off the upright, so 
that it is level with the top 
of the upper coil. Take two 
clips, and fasten the slotted end 
of each under the locking nut of 
a terminal on the top end of the 
coil. Then holding the coil 
close to the upright, attach the 



-244- 



(4) Terminals 




clips to it with small screws 
(F). 

Use bolts (G) and nuts (H) to 
make two terminals, as described 
under VIII/A2, Component (4) . 
Attach them to the front of the 
base. Finally connect the 
terminals and coil holders by 
magnet wire (I) so that electri- 
cal connections exist between 
points a to a, b to b, and c to 
c (see diagram), thus insuring 
that current will flow through 
the multipurpose coils in the 
same direction once the terminals 
at the front of the base are 
connected into a circuit. 



c. Notes 

(i) The apparatus may be used to study the relationship between the force 
exerted on a current carrying conductor and the magnetic field surrounding the 
conductor. For this purpose a suitable magnetic field may be created by connecting 
two dry cells (1.5 volts each) and a torch bulb in series with the multipurpose 
coils. A strong current may be passed through the lightweight roller by momen- 
tarily connecting three dry cells in series with the terminals leading to the 
horizontal rods. Under such conditions the roller will be propelled along the 
rods. 



X. GALVANOMETERS 

A. ELEMENTARY GALVANOMETERS 

These are extremely simple instruments which illustrate the elementary principles 
of galvanometry . They may be used as simple measuring devices, but are not designed 
for accuracy of measurement. 

B. FUNCTIONAL TANGENT GALVANOMETERS 



These instruments are probably the most suitable for general use in the school 
laboratory. They are simple to make and more durable than moving coil galvanometers. 
In addition, they are surprisingly sensitive, and with the help of shunts may be used 
for a multiple range of measurements. 

C. FUNCTIONAL MOVING COIL GALVANOMETER S 

These instruments are quite sensitive, and with the help of shunts may be used 
for a multiple range of measurements. 



A. ELEMENTARY GALVANOMETERS 



Al . Elementary Tangent Galvanometer 



(1) Base 



(2) Coil 




(3) Magnetic 

Needle 



(4) Terminals 



a. Materials Required 
Components 

(1) Base 

(2) Coil 



0) Magnetic 
Needle 



(4) Terminals 



q u Items Required 
Wood (A) 

Maqnet Wire (B) 
Maskinq Tape (C) 
Screw (D) 
Washer (E) 

Needle (F) 
Cotton Thread (G) 

Bolts (H) 
Nuts (I) 



Dimensions 
7cmx7cmxlcm 

#26, 400 cm lonq 
1 cm lonq 

0.1 cm diameter 
5 cm lonq 

0.3 cm diameter, 
2.5 cm lonq 

. 3 cm internal 
diameter 



-247- 



b. Construction 

(1) Base 

(2) Coil 




Cardboard 
Form 



Make the base out of wood (A) . 

Wind 20 turns of the magnet wire 
(B) around a cardboard form to 
make a rectangular coil (5 cm x 
3 cm) , leaving about 5 cm of 
free wire at either end of the 
coil. 



(3) Magnetic Needle 



(4) Terminals 



Remove the coil from the form, 
and wrap sufficient masking 
tape (C) around the coil to 
insure that it maintains its 
shape. Then separate the wind- 
ings slightly on the bottom side 
of the coil, mount the coil on 
the base with the help of a 
washer (E) and a screw (D) 
passed through the separated 
windings . 

Magnetize a needle (F) with the 
help of a magnetizing coil 
(IX/A1) . Cut off about 4 cm of 
the needle, and suspend it 
horizontally at the middle of 
the coil by means of a cotton 
thread (G) attached to the top 
of the coil. 

Use the bolts (H) and nuts (I) 
to make two terminals in the 
base as described under item 
VIII/AZ, Component (4) . Clean 



-iiv- 



the ends of the coil wire with 
sandpaper, and fasten the wires 
to the terminals. 

c . Notes 

(i) Prior to using this apparatus it should be set so that the needle is sus- 
pended in the plane of the coil. A current passed through the coil will cause 
the needle to be deflected away from the plane of the coil, the deflection depend- 
ing on the magnitude of the current carried by the coil. The apparatus simply 
illustrates the principle of the tangent galvanometer, and is too crude for 
specific measurements. 



A2 . Repulsion Type Galvanometer 



(2) Coil 




(3) Repulsion Vane 
Assembly 



a. Materials Required 
Components 
(1) Base 



(2) Coil 



(3) Repulsion Vane 
Assembly 



q u Items Required 

1 Wood (A) 

2 Bolts (B) 

4 Nuts (C) 

1 Cardboard Sheet (D) 

Maskinq Tape (E) 

1 Roll of Maqnet Wire (F) 

1 Aluminum Sheet (G) 

4 Screws (H) 

1 Galvanized Iron Sheet (I) 

1 Galvanized Iron Sheet (J) 

1 Needle (K) 



Dimensions 

10 cm x 10 cm x 1 cm 

0.3 cm diameter, 
2.5 cm lonq 

0.3 cm internal 
diameter 

20 cm x 3.5 cm 



#26, (diameter 0.05 
cm) , 30 meters lonq 

7 cm x 4 cm x . 02 cm 
1 cm lonq 

7 cm x 3.5 cm x 0.02 cm 

4.3 cm x 2.5 cm x 
0.02 cm 

8 cm lonq, . 1 cm 
diameter 



Maskinq Tape (L) 



b. Construction 
(1) Base 



-<ou- 

Soda Straw (M) 
Cardboard Sheet (N) 




Wood (A) 



12 cm x 12 cm 

Make two terminals from bolts 
(B) and nuts (C) [as described 
under VIII/A2, Component (4)] 
and attach them at about 2 cm 
from the edge of the wood (A) . 
The boltheads of the terminals 
should be countersunk into the 
base, so that the latter sits 
flat on any horizontal surface. 



Top View 



(2) Coil 



Mi 

Winding 
Block 



Razor Cut Lines 



Cardboard (D) 



Cut a piece of wood (5 cm x 5 cm 
x 5 cm) to serve as a winding 
block for the coil. Use a 
razor blade to score parallel 
lines on the cardboard (D) at 
5 cm intervals so that it may be 
readily bent into the shape of 
the wooden block. 



Winding Block 




Cardboard (D) 



Wrap the cardboard loosely 
around the block fastening the 
two loose edges together with 
masking tape (E) . 



Masking Tape (E) 



-251- 



Masking 
Tape (F) 



rf^jQjTri^ 




Last Layer 
' of Coil 



Cardboard (D) 




Al umi num 

Sheet (G) 



Coil 



Wind approximately 150 turns of 
the magnet wire (F) onto the 
cardboard form. This will take 
three layers of turns. After 
winding the turns, remove the 
cardboard holder (and turns) 
from the winding block, and 
cover the turns with masking 
tape (E) to hold the wire in 
position. Make sure that about 
10 cm of wire is free at both 
ends of the coil. 

Drill two holes (diameter 0.2 
cm) at either end of the 
aluminum sheet (G) . Set the 
coil in a vertical plane on the 
base, and strap it in position 
with the help of the aluminum 
sheet (G) and four screws (H) . 
Bare the ends of the wire, and 
attach them to the terminals on 
the base. 



(3) Repulsion Vane Assembly 



0.5_ 
0.5_ 

4 


! 

2 
i 








-2.5 ■ 



0.1 
0.5 



Completed Fixed 
Vane 



Two vanes are required, one 
fixed and one free swinging. 
The fixed vane may be cut from 
a sheet of galvanized iron (I) 
according to the dimensions 
indicated. The cut sheet 
resembles a vertical cross. 
Drill a hole (0.2 cm diameter) 
in the top edge of each of the 
horizontal portions of the cross 
(see illustration) . Then bend 
the sheet at right angles along 
the lines indicated. 



Pattern 



-252- 



Masking Tape (L) 

/ 

Pro.iection 



Coil 




The completed vane may then be 
fixed vertically in position 
within the coil by wrapping 
masking tape (L) around the top 
of the coil, covering the 
horizontal portion of the fixed 
vane in the process. 



Fixed Vane (I) 



Needle (K) 



Free 

Swinging 
Vane (J 




Masking Tape (L) 



The free swinging vane is made 
from the other sheet of 
galvanized iron (J) and sus- 
pended from the middle of the 
needle (K) by wrapping a piece 
of masking tape (L) over the end 
of the vane. Suspend the vane 
from the projections on the fixed 
vane . 




Scale (N) 



Back View 



Make a pointer from the straw 
(M) , and pivot it on the needle 
(K) at about 2 cm from the end 
of the straw. Make the scale 
from the cardboard (N) , bending 
the bottom of the scale at 
right angles to form a hori- 
zontal flap. Use masking tape 
to attach the flap (and hence 
the scale) to the top of the 
coil. 




Free Swinging 
Vane 



Fixed 

Vane 



c. Notes 

(i) The ga vanometer may be calibrated by placing it in series with an ammeter 
(0-5 amps), a voltage supply (dry cells, battery, etc.) and a variable resistance 

(ii) The resulting scale will be nonuniform, the separation of points on the 
scale increasing with increasing amperage. The range of the scale for this 



-254- 



particular design will be approximately to 3 amps (DC) . 

(iii) The galvanometer will measure both DC and AC current equally well, since 
the repulsion of the vanes is independent of the direction of the current in the 

coil. 

(iv) The resistance of the galvanometer is approximately 2.5 ohms. The current 
existing in a circuit will therefore be affected in general by the addition of 
the galvanometer to the circuit. 



A3. Hot Wire Ammeter 



(3) Wiring 




Front 
View 



(4) Spring 

System 




i) Support 



2) Pulley 
System 



a. Materials Required 
Components 
(1) Support 



(2) Pulley System 



(3) Wiring 



q u Items Required 

1 Wood (A) 

1 Wood (B) 

2 Screws (C) 
2 Bolts (D) 

4 Nuts (E) 

2 Aluminum Sheets (F) 

4 Screws (G) 

1 Needle (H) 

1 Wooden Dowel (I) 

1 Soda Straw (J) 

1 Cardboard Sheet (K) 

2 Eye Screws (L) 

3 Wood Screws (M) 
2 Washers (N) 

1 Nichrome Wire (0) 



Dimensions 

20 cm x 12 cm x 2 cm 

12 cm x 12 cm x 2 cm 

3 cm long 

0.3 cm diameter, 
3.5 cm long 

0.3 cm internal 
diameter 

5 cm x 2 cm x 0.05 cm 

1 cm long 

5 cm long, 0.1 cm 
diameter 

0.5 cm diameter, 
1 cm long 

12 cm x 6 cm 



1.5 cm long 



#30, 22 cm long, 
0.02 cm diameter 



Copper Wire (P) 



#24, 50 cm long 



(4) Spring System 



Construction 



(1) Support 



Wood 



Screw (C 



(2) Pulley System 



: 


Wood (Q) 


: 


Steel Wire (R) 


i 


Screw (S) 


i 


Thread (T) 


i 


Paper Clip (U) 



Wood (A) 




Terminal 



Metal Plate (F 



Screw (G) 




Support (A) 



Hole in 

Support 



2 cm x 2 cm x 1 cm 

#16, diameter 0.12 cm, 
length 12 cm 

1 cm long 

10 cm long 

Approximately 1 cm 
long 



Attach the vertical component 

(A) to the middle of the base 

(B) with the help of screws (C) 
and wood cement. 

Use the bolts (D) and nuts (E) 
to make two terminals [as 
described under VIII/AZ, Com- 
ponent (4)] and attach these to 
the front of the base. The 
boltheads of the terminals 
should be countersunk into the 
bottom of the base (B) so that 
the latter sits flat on any 
horizontal surface. 

Drill a hole (diameter 0.5 cm) 
through the exact middle of 
the vertical component (A) of 
the support. Drill a hole 
(diameter 0.2 cm) through the 
center of each of the aluminum 
plates (F) to serve as pivot 
holes for the pointer. Drill 
two holes (diameter 0.2 cm) in 
diagonally opposite corners of 
each plate, so that the latter 
may be screwed onto either side 
of the support over the 
centrally drilled hole. The 
holes in the plates should be at 
the same height on both sides of 



Support (A) 



Metal 
Plate (F> 



Straw (J) 




\ 



Needle (H) 



the support, so that the needle 
(H) may be pivoted horizontally 
through the holes. 

Use a file and sandpaper to 
make a groove in the wood dowel 
(I) forming a pulley, thus pre- 
venting string from slipping 
off it. Drill a small hole in 
the end of the pulley (I) so that 
it may be slipped onto the end 
of the needle (H) , and fix it 
firmly in position with the 
help of glue. 

Make a pointer from the soda 
straw (J) and attach it to the 
needle about 2 cm from the end 
of the straw. 



Cross Section 



Cut a semicircular scale 
(diameter 12 cm) out of card- 
board (K) , and glue it to the 
vertical support behind the 
pointer. 



-Z5V- 



(3) Wiring 



Washer (N) Screw < M > 




Jack View 



Eye 
Screw (L) 



Nichrome 
Wire (0) 



0.5 



Copper 
Wire (P) 



-Eye Screw (L) 



' Copper 

Wire (P) 



Fix two eye screws (L) into the 
rear right-hand side of the 
support. About 2 cm to the 
left of each eye screw fix a 
small wood screw (M) and a 
washer (N) . 

Connect the nichrome wire (0) 
from one wood screw, through 
both eye screws, to the other 
wood screw. The length of the 
wire should be adjusted so that 
it needs to be pulled about 
0.5 cm from the vertical, at 
its center point, in order to 
make it completely taut. 

Drill two holes in the vertical 
component of the support to 
carry electrical wire from the 
rear of the support to the 
front. Make one hole (0.2 cm 
diameter) through the support 
about 1 cm beneath the bottom 
wood screw and a second hole 
at the same height, but on the 
left side of the support. 
Connect a length of copper 
wire (P) from the lower wood 
screw, through the nearest hole 
in the support, to the nearest 
terminal at the front of the 
base. Connect a second length 
of wire (P) from the upper wood 
screw, through the second drill 
hole, to the remaining terminal. 
It is convenient to keep the 
second copper wire away from the 
middle of the support and the 
pulley system, with the help of 
a third wood screw (M) . 



-259- 



(4) Spring System 



Wood (Q) 



Screw (S) 



Wire (R> 




Paper Clip (U) 



(T) 



Back View 



Attach the small wood block (Q) 
to the rear of the support at 
the top left-hand corner. Insert 
a screw (S) into the block and 
fasten the end of a length of 
steel wire (R) between the screw 
and block so that the wire is 
held rigidly in a vertical 
position, thus serving as a 
spring. 

Attach the thread (T) at one 
end to the middle of the hot 
wire (0) with the help of a 
small paper clip (U) . Wrap the 
thread around the pulley (I) 
once, and then tie the free end 
onto the spring wire (R) . In 
order to do this make a small 
kink in the steel wire at the 
point of attachment of the 
thread, thus preventing the 
latter from slipping, and 
during the tying of the thread, 
make sure that the spring wire 
is pulled towards the hot wire. 
This insures that the thread is 
always under tension, and that 
the pulley (and hence pointer) 
responds readily to any move- 
ment of the hot wire. 



c . Notes 

(i) The galvanometer may be calibrated by placing it in series with an amneter 
(0-5 amps), a voltage supply (dry cells, battery, etc.) and a variable resistance. 

(ii) The resulting scale will be nonuniform, the separation of points on the 
scale increasing with increasing amperage. The range of the scale for this parti- 
cular design will be approximately to 1.5 amps (DC). 



(iii) The galvanometer will measure both DC and AC current equally well, since 
the extension of the hot wire (and hence the movement of the pointer) is dependent 
on the heating of the wire, which in turn is proportional to the square of the 
current passing through the wire. 

(iv) The resistance of this galvanometer is approximately 4.5 ohms. 



A4 . Current Balance 



2) Balance Arm 



(3) Coil 




1) Base 



a. Materials Required 
Components 
(1) Base 



(2) Balance Arm 



(3) Coil 



Qu I tems Required 
Wood (A) 
Wood Strip (B) 
Aluminum Sheet (C) 
Screw (D) 

Needle (E) 
Soda Straw (F) 



1 


Nail (G) 


1 


Magnet Wire (H) 


— 


Masking Tape (I) 


2 


Pins (J) 


l 


Sheet of Paper (K) 


l 


Cardboard Sheet (L) 


: 


Magnet Wire (M) 


— 


Masking Tape (N) 


2 


Bolts (0) 



Nuts (P) 



Dimensions 
22 cm x 5 cm x 2 cm 
6 cm x 2 cm x . 5 cm 
10 cm x 2 cm x 0.05 cm 
1 cm long 

4 cm long, . 1 cm 
diameter 

21 cm long, 
approximately 

. 4 cm diameter 

#30, 10 cm long 



10 cm x 2 cm 

2 c m x 2 c m 

#22, 400 cm long 



0.3 cm diameter, 
3.5 cm long 

0.3 cm internal 
diameter 



-262- 



b. Construction 
(1) Base 



Pivot Support (C) 




Wood (B) 




Base (A) 



Fasten an upright piece of wood 
(B) to the rear of the base (A) , 
and to one side. Make a pivot 
support from the sheet of alumi- 
num (C) . Drill a hole (diameter 
0.2 cm) in the middle of the 
horizontal portion of the 
support, and attach it to the 
base with the screw (D) . 



— ■■ v 




1 

4 




/ 


T 



Using a small file cut a 
shallow, smooth notch in the 
top of each side of the support 
to hold a subsequent needle 
pivot in position. 



Pivot Support (C) 



(2) Balance Arm 



Straw (F) 



/ 




2 



Needle (E) 



Insert the needle (E) through 
the top edge of soda straw (F) 
at a distance of 7 cm from one 
end. Balance the straw on the 
support . 



Masking 
Tape (I)' 




-Wire (H) 



•Nail (G) 



Cut two lengths from the nail 
(G) , one 1 . cm long and one 
2.0 cm long. Attach a three 
centimeter-long loop of the 
magnet wire to the end of 
each nail with the help of a 
strip of masking tape 



-263- 



Nails 



Magnet 
Wire (H) 



Straw (F) 




Pins (J) 



Needle (E 



(3) Coil 



C3 



-Paper (K) 



.Wooden 
Dowel 



the short nail at the end of the 
short arm of the straw, and hang 
the long nail at an appropriate 
point on the other side of the 
pivot to serve as a counter- 
balance. A drop of glue (or a 
small piece of masking tape) can 
insure that the loops do not 
slip along the straw. 

With the straw balanced hori- 
zontally note the corresponding 
point on the upright (B) . 
Insert two pins (J) horizontally 
into the upright, one pin 0.5 
cm above the top surface of the 
balanced straw, and the other 

. 5 cm below the bottom surface, 
thus restricting the motion of 
the end of the straw to about 

1 cm. 

Set a length of magnet wire (M) 
on the straw to serve as a 
rider (see notes) . 

Wrap the paper (K) around a 
wooden dowel (1.0 cm diameter) 
to make a paper cylinder. 
Secure the Joose ends of the 
paper with masking tape (N) . 



Paper 
Cylinder 




Cardboard 
Washers 



Dowel 



Cut two washers (internal 
diameter 1.0 cm, external 
diameter 2.0 cm) from the sheets 
of cardboard (L) . Attach the 
washers to the ends of the 
paper cylinder with glue. 



Pointer 




Coil 



Terminals 



c. Notes 



Wind the magnet wire (M) onto 
the paper cylinder to make a 
coil. Leave 10 cm of wire free 
at either end. Cover the last 
layer of wire with masking tape 
(N) to hold the coil in position. 
Remove the coil from the dowel, 
and mount it on the end of the 
base with glue in such a way 
that the axis of the coil is 
directly beneath the nail sus- 
pended from the end of the straw 
balance arm. 

Drill two holes (diameter 0.3 cm) 
in the base at any convenient 
point close to the .coil, and 
make two terminals from the 
nuts (P) and bolts (o) as 
described under VIII/A2, Com- 
ponent (4). Fit the terminals 
in the two holes, and connect 
the wires from the coil to the 
terminals . 



(i) The galvanometer may be calibrated by placing it in series with an ammeter, 
a voltage supply and a variable resistance noting the position of the rider each 
time the straw balance arm is balanced and noting simultaneously the corresponding 
current through the coil. 



-265- 



(ii) A whole range of different scales may be produced simply by changing the 
mass of the rider on the balance arm. One such scale is illustrated below when 
the rider used was a 25 cm length of #26 magnet wire coiled into a loop, approxi- 
mately 1 cm diameter. 



"I 



Pi 



/ 



0.7 I 0.9 i 1.1 I 1.3 i 
i i i f i 



~i — r 



1 t iTt 

0.8 1.0 1.2 1.4 



Arrps (DC) 



Attracted 

Nail 



Rider 



(iii) The resultant scale on the straw is linear . In Other words, doubling the 
current passing through the coil doubles the force exerted by the coil on the 
nail, and the distance between the rider and pivot must be doubled to reestablish 
the balance of the straw. 

(iv) The galvanometer will measure AC and DC currents egually well since the 
direction of the attraction exerted by the coil is not dependent on the direction 
of the current through the coil. 



(\) The resistance of the galvanometer is approximately 0.1 ohms, 



A5 . Elementary Moving Coil Galvonometer 



(4) Scale 




(1) Base 



(3) Magnet 



(2) Moving Coil 



a. Materials Reguired 
Components 
(1) Base 



(2) Moving Coil 



(3) Magnet 



(4) Scale 



U Items Reguired 

1 Wood (A) 

2 Bolts (B) 

4 Nuts (C) 

2 Coat Hanger Wire (D) 

1 Roll of Magnet Wire (E) 

1 Coat Hanger Wire (F) 

1 Masking Tape (G) 

2 Thumbtacks (H) 

1 Horseshoe Magnet (I) 

2 Wood Strips (J) 

1 Straw (K) 

1 Cardboard Sheet (L) 



Dimensions 

14 cm x 13 cm x 1.5 cm 

. 3 cm diameter, 
3.0 cm long 

0.3 cm internal 
diameter 

7 cm long, 0.2 cm 
diameter 

#26 

10 cm long, . 2 cm 
diameter 



Approximately 8 cm x 
1.5 cm x 1.0 cm 

6 cm long 

10 cm x 10 cm 



b. Construction 



(1) Base 




Make two terminals [see VIII/A2, 
Component (4)] from the nuts (C) 
and bolts (B), making sure to 
inset the boltheads into the 
bottom of the wood (A) . Drill 
two holes (0.2 cm diameter, 1.0 
cm deep) into the base to hold 
the vertical supports. 



Wood (A) 




wire (D) 



Side View 
(Cross-section) 



Make two vertical supports for 
the coil by twisting the coat 
hanger wire (D) into the shape 
indicated. Set the supports 
vertically upright in the newly 
drilled holes in the base. 



(2) Moving Coil 



Coil 




Cardboard Form 



Coil 




'Axle (F ) 



Wind 30 turns of magnet wire (E) 
around a cardboard form in order 
to make a coil of internal 
size 3.5 cm x 1.5 cm. Leave 
100 cm of wire free at either 
end of the coil. 



Thread the wire (F) through the 
middle of the coil to serve as 
the axle for the coil. Wrap 
masking tape (G) around the 
coil and axle to hold the coil 
firmly in position. 



100 cm Ends 



Springs 



Masking 
Tape (G) 




Thumb Tack (H) 



Coil Support 



Fit the coil (F) into the coil 
supports (D) on the base. Wind 
the 100 cm of magnet wire (E) at 
either end of the coil into a 
spring, and attach the wire, 
just beneath each spring, to the 
base with the help of a thumb- 
tack (H) . Each spring should 
contain about eight turns and 
be about 3 cm in diameter. 



Coil Support 



Thumb 
Task (H) 




Terminal 



(The sensitivity of the moving 
coil increases with increasing 
number of turns and increasing 
diameter of the spring.) Connect 
the wire from the springs to the 
terminals on the base. 



Top View 



(3) Magnet 



Top View 




Prevent slipping of the axle 
on the supports by wrapping 
masking tape around the 
axle either side of one of the 
supports . 

Procure a horeseshoe magnet (I) 
with pole heads at least 4 cm 
apart, and place it as shown 
around the coil. Make two 
wooden strips (J) which, when 
placed under the magnet, will 
bring the pole heads up to the 
same height as the coil. The 
ends of the magnet should be 
located opposite the middle of 
the coil. 



Wood Strips (J) 



(4) Scale 




Take the straw (K) and, after 
piercing it 1 cm from one end, 
fit it on the end of the axle. 
A little glue will fix it 
firmly in position. Cut a 
suitable scale out of cardboard 
(L) , and attach it to the base, 
so that it stands just behind 
the pointer . 



c. Notes 

(i) The galvanometer may be Calibrated by placing it in series with an ammeter, 
a voltage source and a variable resistance. The sensitivity of the galvanometer 
will depend very much on the strength of the horseshoe magnet used. 

(ii) The galvanometer will measure DC current, but not AC. 

(iii) Ifa suitable horseshoe magnet is not available, an electromagnet may 
readily be made. To do this, take a soft iron bar (17.5 cm x 2.0 cm x 0.3 cm), 

and bend it into a horseshoe 

4.5 — -| 

1.0 



I— 



Coil' 



IT 

4 

i 



': - 



^ 



l.S 



h=^P 



Coil 



shape as indicated. Take about 
100 g of #26 magnet wire, and 
wind a coil on each side of the 
U-shaped bar. Each coil should 
be about 4 cm long, and should 
contain ten layers of wire. 
The coils should be connected 



Iron 
Bar 



■ Connecting 
Turns 



in series to one another, simply 
by continuing the windings in 
the same direction around the 
bar from one coil to the other 
in a series of widely spaced 
connecting turns. The coils may be held in position by means of masking tape. If 
the coil is connected in series into a separate electrical circuit, it may be 
used in precisely the same way as the former horseshoe magnet. 



-271- 



(iv) With a current of 0.5 amps through the electromagnet coils, a 2-amp current 
through the moving coil produced a deflection of approximately 30°. When the 

current through the electro- 
magnet was increased to 1.0 amp, 
the deflection, due to a 3-amp 
current through the movingcoil, 
increased to 45° . 




Electromagnet Current Of Lamp 



FUNCTIONAL TANGENT GALVANOMETERS 



Bl. Tangent Galvanometer 



© 




(1) Support 



(3) Terminal 



(4) Compass 



(2) Coil 



a. Materials Required 
Components 
(1) Box Support 



(2)Coil 



(3) Terminals 



(4) Compass 



Qu 

: 

2 

1 



1 



Items Required 
Wooden Base (A) 
Wooden Sides (B) 
Wooden Platform (C) 
Small Wood Screws (D) 

Roll of Magnet Wire (E) 
Varnish (F) 

Brass Bolts (G) 
Nuts (H) 

Wood Disc (I) 



3 Needles (J) 
1 Brass Rod (K) 



Dimensions 
12cmx6cmxlcm 
6cmx2cmxlcm 
12cmx6cmxlcm 
1.5 cm long 

#24 



0.3 cm diameter, 
2 cm long 

0.3 cm internal 
diameter 

2.5 cm diameter, 
0.3 cm thick 

0.1 cm diameter 

0.5 cm diameter, 
0.5 cm long 



© From Reginald F. Melton, E lementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 1972), pp 143-145. 



b. Construction 
(1 (Support 




Hole Inset 



Hole 




Make a four-sided wooden support 
from the wooden base (A) , 
wooden sides (B) and platform 
(C) . Fasten the base and sides 
together with small screws (D) 
and wood cement, but do not put 
the platform in position yet. 

Drill an inset (2.5 cm diameter, 
. 2 cm deep) into the middle of 
the platform, and two holes 
(1 cm diameter) right through 
the platform to take the coil. 
Cut the platform into two equal 
halves, fastening one half 
only in position with small 
screws and wood cement. 



(B) Half Platform (C) 



(2) Coil 



Bolt & 
Wingnut 




Sidepieces 



Block 



To make the coil a simple 
winding device is desirable. 
This may be made from a block 
of wood (5 cm x 5 cm x 1 cm) 
and two cardboard sides ( 8 cm x 
8 cm x 0.5 cm) . Drill a hole 
through the middle of the block 
and sides and hold the parts 
together with a bolt and wing 
nut. 

Wind 100 turns of magnet wire 

(E) onto the block, layer by 
layer, adding a coat of varnish 

(F) to each layer to hold the 
turns together. Make sure that 
about 20 cm of both ends of the 




wire are left free to make 
appropriate connections. 

When the varnish is dry remove 
the coil from the block (simply 
by releasing the sides) and 
sit the coil vertically in the 
support . 

Attach the second half of the 
platform with small wood screws 
and wood cement . 



(3) Terminals 



(4) Compass 



Magnetic 

Needles (J) 




Base (I) 



Cap (K) 



Pivot 
Needle (J) 



Use bolts (G) and nuts (H) to 
make two terminals as described 
under VIII/A2, Component (4) . 
Fix one on either side of the 
support, and attach the two 
wires from the coil to the 
terminals. Don't forget to 
clean the ends of the wire with 
sandpaper. 

Use the wood disc (I) as the 
base of the compass. Alterna- 
tively, a cork disc would serve 
egually well, although less 
durable . 

Cut a 1 cm length off the 
pointed end of a needle (J) . 
Drill a small hole (0.1 cm 
diameter) in the middle of the 
base and set the needle in the 
hole with epoxy resin so that it 
stands vertically, pointed end 
uppermost . 



-275- 




Cap (K) 




Solder 



Needles (J) 



c. Notes 



Holding rod (K) firmly in a 
clamp, drill a hole (0.3 cm 
diameter) . 3 cm deep along the 
axis. You now have a suitable 
cap to sit on the pivot. 

Cut 2 cm lengths off the two 
remaining needles (J) . Deter- 
mine the center of gravity of 
each by balancing the needles 
over another needle. Mark in 
the position of the center of 
gravity of each of the two 
needles. 

Hold the needles parallel to 
one another and drop some 
solder on the base of the cap. 
Innnediately attach the needles 
(at their centers of gravity) 
to the cap by placing them in 
the still molten solder. 

Finally, place the cap and 
needles inside a magnetizing 
coil (IX/A2) to magnetize them, 
and then place them on top of 
the pivot. 

Note the ends of the needles 
which point to the North, and 
mark these (e.g., with paint). 



(i) The galvanometer should be set so that the plane of its coil is in a North- 
South direction, as indicated by the compass needle. A current passing through 
the coil will cause the needle to be deflected out of this plane, the angle of 
deflection depending on the strength of the current. 

(ii) It is important that magnets and iron should be kept well away from the 
galvanometer during use to avoid influencing the compass needle. 

(iii) The galvanometer will readily detect the differences in magnitude of currents 
produced by the various combination of plates and electrolytes in the Chemical 
Cell (VIII/A1) . 



-276- 



B2 . Tangent Galvanometer with Shunts * 



(2) Coils 



(3) Magnetic Needle 
Assembly 



(1) Base 




(4) Shunts 



a. Materials Reguired 
Components 
(1) Base 



(2) Coils 



U Items Reguired 
1 Wood (A) 



2 



Bolts (B) 



4 Nuts (C) 

2 Wood (D) 

2 Wood (E) 

1 Magnet Wire (F) 

Masking Tape (G) 



Dimensions 

10 cm x 10 cm x 
1 cm 

0.3 cm diameter, 
2.5 cm long 

0.3 cm internal 
diameter 

8 cm x 5 cm x 
0.5 cm 

3 cm x 5 cm x 
0.5 cm 

#26 (diameter 0.05 
cm) , length approx- 
imately 16 meters 



*Adapted from Fr. George Schwarz, A Don Bosco Laboratory Manual, (Philippines: 
Unpublished Papers). 



-277- 



(3) Magnetic Needle 
Assembly 



: 



Needle (H) 

Razor Blade with 
Double Edges (I) 

Glass Tube (J) 



2 Screws (K) 

1 Cardboard Sheet (L) 

1 Pin (M) 



10 cm long, 0.1 
cm diameter 



6 cm long, . 5 

cm external diameter 

1.5 cm long 

2.5 cm x 2.0 cm 

2.5 cm long, approx- 
imately 



(4) Shunts 



b. Construction 
(1) Base 



3 Cardboard Sheets (N) 

1 Nichrome Wire (0) 

1 Resistor (P) 

1 Bolt (Q) 

1 Nut (R) 



B cm x 4 cm 

#24, 0.17 ohms 
(approximately 
5 cm long) 

1,000 ohms (from 
radio shop) 

0.3 cm diameter, 2.5 cm 
long 

0.3 cm internal 
diameter 



Drill two holes (diameter 
0.3 cm) in Wood (A) about 3 cm 
apart and close to one edge to 
take the terminals. Use bolts 
(B) and nuts (C) to make two 
terminals as described under 
VIII/A2, Component (4), and fit 
them through the holes in the 
base. The boltheads should be 
countersunk into the bottom of 
the base so that the latter sits 
flat on any horizontal surface. 



-276 



(2) Coils 



Coils (F) 




Make a wooden form using wood (D) 
for the top and base and wood (E) 
for the side pieces. Glue the 
pieces together. 

Drill a hole (1.0 cm diameter) 
in the middle of the top, and an 
identical hole (1.0 cm diameter) 
directly beneath in the middle 
of the base of the form. 

Wind magnet wire (F) around the 
form to make two coils which 
are connected in series to one 
another, and which are wound in 
the same direction around the 
form. Wind 20 turns of wire 
into each coil, and locate these 
close to the opposite edges of 
the form. Make sure that about 
10 cm of each end of the wire 
is left free. After winding 
the coils, cover the final layer 
of turns with a layer of masking 
tape (G) to hold the coils in 
position. 



Position of 
Coil Form 




Drill two appropriate holes 
through the base in order to 
attach the coil form to the base 
with screws, but do not screw 
the form on to the base yet. 



Terminals 



-279- 



(3) Magnetic Needle Assembly 




Small Hole 
in Base 



Drill a hole (0.1 cm diameter) 
in the base in the position that 
corresponds to center of the 
larger hole in the base of the 
coil form. Cut the end (con- 
taining the eye) off needle (H) 
to make it 8 cm long, and set 
the blunt end of the needle 
firmly in the hole in the base, 
so that it stands vertically 
with the point upwards. A little 
epoxy resin may be required to 
hold the needle firmly in the 
hole. 






Center Hole 



Tube (J) 




Heat 
Closed 



Take a double-edged razor blade 
(I) which contains a center hole, 
and magnetize it with the help 
of a magnetizing coil (IX/A1) . 
Measure the size of the center 
hole (probably about 0.5 cm 
diameter) , and take a glass tube 
(J) with the same external diameter 
as that of the center hole. Heat 
close (CHEM/I/D5) one end of the 
tube and create flanges (CHEM/I/ 
D7) at the open end. The flanges 
on the tube will prevent the razor 
blade from slipping off the tube, 
so long as the latter is held in 
a vertical position. 



Flanged 



-280- 




Razor 
Blade (I' 



To put the magnetic needle 
assembly together, hold the razor 
blade horizontally inside the 
coil form. Insert the glass 
tube through the base hole in 
the form, and then through the 
hole in the blade. 



Form 




Lower the blade onto the 
flanges of the glass tube, and 
raise the tube partially 
through the upper hole in the 
form. 



Needle (H) 




Screws 



Lower the coil form and tube 
together onto the needle pro- 
jecting vertically from the 
base. Take two screws (K) and 
firmly attach the base and 
coil form together. 

Connect the loose wires from the 
coils to the terminals, making 
sure that all enamel has been 
removed from the wire ends. 




0.5 



Sheet (L) 




Take the thin sheet of cardboard 
(L) , and thrust pin (M) through 
the sheet at about . 5 cm from 
the middle of the top edge. Bend 
the cardboard around the glass 
tube (J) to form a tight cylinder 
from which the full length of the 
pin will protrude. Fasten the 
free ends of the cardboard sheet 
together with masking tape wrap- 
ped around the cylindrical sheet. 



Lower the cardboard cylinder onto 
the tube until it touches the 
razor blade. The pin should 
clear the top of the form by 
about 0.5 cm, and will serve as 
a pointer to record the motion 
of the magnetized needle below. 



Cylinder (L) 




Scale (N) 



Pointer (M) 



Cut a semicircular disc (diameter 
B cm) out of the cardboard 
sheet (N) , and set it on top of 
the coil form to serve as a 
scale. Mark the position of the 
cardboard on top of the form, 
SO that the cardboard scale may 
be replaced in exactly the 

same position whenever it is 

removed. 



-282- 



(4) Shunts 



Terminal 



1.5 n 



■©■ 



Terminal 

t « loi 

-» — o ►— 



0.17 ft 



Set the plane of the galvanometer 
coils in a North-South direction 
so that the longitudinal, 
horizontal axis of the magnetized 
razor blade is in the same plane 
as that of the coils. The 
direction of the pointer should 
be set at 90° to this plane. 
Now calibrate the galvanometer 
by placing it in series with a 
milliamneter (0-100 milliamps) , 
a voltage supply (dry cells, 
battery, etc.) and a variable 
resistance. The resultant 
scale will swing from the center 
zero position of the pointer 
through about 90°. If the 
direction of the current through 
the coil is reversed, a deflection 
(and hence scale) in the opposite 
direction will be obtained. 



Base 



Coils 




Shunt 
0.17 n 



External 
Circuit 



Terminal 



Take a suitable length of 
nichrome wire (0) and connect 
it across the galvanometer ter- 
minals. In this case, since 
the resistance of the galvanometer 
is 1.5 ohms a wire of resistance 
0.17 ohms (5 cm of #24, U.S. 
Standard Plate guage, nichrome 
wire, 20% chrome, 80% nickel) 
would result in 1000 milliamps 
(1 amp) producing a full scale 
deflection instead of 100 
milliamps doing this. 



Top View 



-283- 



With the resistance wire across 
the terminals recalibrate the 
galvanometer in the usual way 
with a fresh cardboard sheet for 
a new scale. 



Base 



Coils 




Resistor 



External 
Circuit 

Voltmeter 



-^v> 



\vWv* 

1,001.5 n 

— © — 

Galvanometer 



4 



' Terminal 



To convert the galvanometer to 
a voltmeter; add a 1,000 ohm 
resistor (P) in series to the 
galvanometer. To do this use 
bolt (Q) and nut (R) to make a 
terminal as described under 
VIII/A2, Component (4), and add 
it to the base between the 
existing terminals. Then 
connect the resistor (obtained 
from a radio shop) across two 
adjacent terminals as illustrated. 
Recalibrate the modified 
galvanometer by placing it in 
parallel across a variable 
resistance, and comparing the 
potential at any moment with a 
commercial voltmeter, also placed 
in parallel with the variable 
resistance. 



-284- 



1.5 a 



f TOO mA 



•M/W- 



V AB =0.15 volts 



l.ooo n 
-4NW— (5)— I 



1.5 n 1 100 m A 
-'VWvAr- 



B 



V AB = 100 volts 



Without a resistance in series, 
the full-scale deflection of the 
galvanometer would only measure 
0.15 volts across the terminals. 
With the 1,000 ohm resistance in 
series, the full-scale deflection 
of the galvanometer would 
measure 100 volts across the 
terminals, More important, the 
current taken through the 
galvanometer, compared with that 
in the circuit being measured, 
would be negligible. 



c. Notes 



(i) The resultant scales will be nonuniform, sensitivity falling off with 

increasing voltage as indi- 
cated. The scale will 
indicate the direction of 
the current through the 
galvanometer. 




(ii) The galvanometer cannot measure AC current. 

(iii) This galvanometer is relatively simple to make, it is surprisingly 
sensitive, and in combination with the shunts may be used for a wide range 
of measurements of amperage and voltage. 



-285- 



C. FUNCTIONAL MOVING COIL GALVANOMETERS 



CI. Moving Coil Galvanometer® 



(4) Moving Coil 



Terminals and 
Admustment Screw 




(5) Scale 



(I) Base and 
Upright 



a. Materials Required 

Components 

(1) Base with 
Upright 



q u Items Required 

1 Wood (A) 

1 Wood (B) 

2 Wood Screws (C) 



Dimensions 

14 cm x 11 cm x 1 en 

6 cm x 11 cm x 1 cm 
2 cm long 



© From Reginald F. Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for EUuudliuiidl Dy vulujJiueiit Oueisedb, — 1972), jjp 103-100 . — 



-286- 



(2) Terminals and 

Adjustment Screw 2 



(3) Magnet 



(4) Moving Coil 



(5) Scale 

b. Construction 

(1) Base with Upright 



Upright (B) 



h? * 



/ 



Screw (C) 



Brass Bolts (D) 

Nuts (E) 

Bolt (F) 

Nut (G) 

Thumbtacks (H) 
Horseshoe Magnet (I) 

Wooden Dowel (J) 

Galvanized Wire (K) 

Needle (L) 

Box of Nails (M) 

Roll of Magnet Wire (N) 
Pieces of Magnet Wire (0) 
Wood Screw (P) 
Brass Strip (Q) 

Wood Screw (R) 
White Paper (S) 



0.3 cm diameter, 
2.0 cm long 

0.3 cm internal 
diameter 

0.2 cm diameter, 
2 cm long 

0.2 cm internal 
diameter 



Separation of poles 
between 3.0 cm and 
3 .5 cm 

2 cm diameter, 

3 cm long 

7.5 cm long, 0.1 cm 
diameter 

0.1 cm diameter, 
5 cm long 

2 cm long, diameter as 
small as possible 

#22 

#30, 50 cm long 

0.8 cm long 

3.5 cm x 1.0 cm x 0.05 
cm 

0.8 cm long 

10 cm x 10 cm 



Base (A) 
I 



Attach the wooden upright (B) 
to the base (A) with two screws 
(C) from beneath the base and 
with wood cement to make a firm 
joint. Leave approximately 
2 cm behind the upright. 



Side View 



(2) Terminals and Adjustment Screw 



Adjustment Screw 

1 



Terminals 

Upright (B) 
Thumbtack "O0 




11 



t 

3ase (A) 



Make two terminals in the front 
of the base from the brass bolts 
(D) and nuts (E) [See VIII/A2, 
Component (4) ] . 

Make an adjustment screw [as 
described under IX/A3, Component 
(1)] from the bolt (F) and 
nut (G) to fit in one side of the 
base. At opposite corners of 
the other side of the base, 
insert two thumbtacks (H) to the 
bottom so that the base is rested 
on three points, the adjustment 
screw and thumbtacks. 



Top View 



(3) Magnet 




Slot 



Obtain a strong horseshoe magnet 
(I) in which the separation of 
the two sides of the horseshoe 
is approximately 3 cm (or a little 
more) . Make slots in the upright 
(B) as illustrated to allow the 
magnet to be pushed through the 
upright so as to protrude a 
distance of 2 cm. Once the 
moving coil (below) has been 
fixed finally in position, fix 
the magnet firmly in the upright 
with epoxy resin. The slots are 
Maanet (I) most easily made before the 

upright has been screwed to the 
base. 



-288- 



(4) Moving Coil 
Core Hole 




Make an inset (0.5 cm wide, 
0.5 cm deep) around the wooden 
dowel (J) specifically to hold 
a coil. Drill a hole (0.8 cm 
diameter) along the axis to take 
the pivot and soft iron core. 



Inset 



Pointer (K) 



Expoxy 
Resin 




Bore a hole (0.5 cm deep, 0.1 cm 
diameter) horizontally into the 
bottom of the core at right 
angles to the plane of the inset 
(and coil} 

Then, fit the galvanized wire (K) 
into the hole with epoxy resin to 
serve as a pointer. 

The needle (L) will serve as a 
pivot. Cut off the heads of the 
nails (M) , and make the length 
2 cm. Pack the nails into the 
hole through the middle of the 
wooden core (J) , placing the 
needle (L) in the very center 
of the hole, so as to protrude an 
equal distance from either end of 
the core. Bind the newly created 
core and pivot firmly in position 
with a liberal coating of epoxy 
resin over the nail ends and 
around the needle. 



-289- 



Spring 
Coil 



Moving 
Coil 



Spring 
Coil! 



upper 

Pivot (q) 



To Terminal 




To Terminal 



Pointer (K) 



Wind 40 turns of magnet wire (N) 
around the inset of the core, 
making sure that both ends are 
left free. Clean the ends of the 
wire with sandpaper and solder 
each end on to another length of 
very fine magnet wire (0) from 
which fine spring coils may be 
made around the top and bottom 
portions of the pivot. 



Screw (P 



To Terminal 




Spring Coil 



The sensitivity of the spring in- 
creases as the number of turns 
wound into the spring increases, 
and as the diameter of the spring 
increases. Once each spring has 
been wound, avoid subsequent 
damage during construction by 
holding it between two pieces of 
cardboard which may be taped to 
the wooden core. 



-zyu- 



Inset 




Screw (P) 



Insert the wood screw (P) into 
the base at a point 2 cm from 
the front of the upright and 
centered. Drill an inset (0.2 cm 
deep) into the head of the screw 
so that it will serve as a lower 
pivot for the coil. 




Screw Hole 



Pivot Hole 



Side View 



Spring 
Coils 




Bend the strip of brass (Q) to 
form an "L" shape. Drill a 
screw hole (diameter 0.3 cm) in 
the short end and a pivot hole 
(diameter 0.2 cm) at a distance 
of 0.5 cm from the other end. 
Slide the strip over the pivot 
needle, and screw the strip to 
the upright, with the screw (R) . 



Connect the wire from the two 
ends of the springs to the two 
terminals, One of the best ways 
of doing this is to drill small 
holes in the upright (opposite 
the springs) threading the wire 
through the holes. If two more 
holes are drilled through the 
upright near the bottom (one on 
either side) the wire may be 
threaded back through the upright 
to the terminals. 



-291- 



(5) Scale Cut a sheet of paper (S) and paste 

±ton the base. Taking the lower 
pivot as the center point, mark 
off a scale to indicate every 
10° movement of the pointer. 
The scale may later be recali- 
brated in amps or volts as 
desired. 

c. Notes 

(i) Should there be any difficulty in obtaining a suitable, strong 
horseshoe magnet, then multipurpose coils may be used as described in the 
next item. 



-292- 



C2. Moving Coil Galvanometer with Multipurpose Coils 



© 



(3) Coil 
Holders 



(2) Multipurpose 
Coils 




(4) Terminals 

and Wiring 



(1) Basic Apparatus 



a. Materials Reguired 

Components qu Items Reguired 

(1) Basic Apparatus 1 Moving Coil 



(2) Multipurpose 2 
Coils 



(3) Coil Holders 



4 
2 

4 



Multipurpose Coil 
with Cores (B) 

Brass Sheets (C) 



Screws (D) 
Brass Sheets (E) 
Screws (F) 



Dimensions 

X/Cl, all components 
except component (3) 

IX/A2 



3.0 cm x 0.8 cm x 
0.05 cm 

0.8 cm long 

2 cm x 2 cm x 0.02 cm 

0.8 cm long 



©From Reginald F Melton, Elementary, Economic Experiments in Physics, Apparatus 
Guide, (London: Center for Educational Development Overseas, 19/2), pp 159-161. 



-293- 



(4) Terminals and 2 Brass Bolts (G) 0.3 cm diameter, 

Wiring 2 cm long 

4 Nuts (H) 0.3 cm internal 

diameter 

1 Roll of Magnet Wire (I) #24 

b, Construction 

(1) Basic Apparatus Make the moving coil galvanometer 

as described under X/Cl, but do 
not make component (3) of the 
item or the holes in the upright 
to take a magnet. The finished 
product will in fact be the 
basic apparatus (A) . 

The subsequent making of the 
coil holders and addition of 
further terminals to the basic 
apparatus is likely to damage 
the moving coil springs unless 
these are carefully protected. 
It is therefore suggested that 
the springs be held between 
cardboard sheets taped to the 
wooden core while further modi- 
fications are made, 

(2) Multipurpose Coils Make two multipurpose coils (B) 

complete with soft iron cores 
and pole heads as described 
under IX/A2. 



(3) Coil Holders 



0.3 



O 



0.6 
_J_ 



Brass (C) 



Clip 
Holder 



Moving 
Coil 



Clip 
HoJldei 




Nut 



Locking 
Nut 



Cut four clip holders from the 
four brass sheets (C) , making a 
screw hole at one end and a small 
slit at the other. Fit the four 
slits in the holders under the 
locking nuts of the four termin- 
als of the multipurpose coils (B) . 
Then position each coil in turn 
on the upright so that the pole 
head is at exactly the same 
height above the base as the 
moving coil core. In this posi- 
tion screw the clips firmly on- 
to the edge of the upright with 
the screws (D) . 



Front View 



0.3 0.3 

Ho.&H 



ihH h 



0.4 



0.4 




Spring 
Holder 



Make two spring holders from 
the two brass sheets (E) and 
slip these on the free ends of 
the multipurpose coils to deter- 
mine where they should be attach- 
ed to the upright. Having marked 
in the position, screw the 



-295- 



holders onto the upright with 
the remaining screws (F) . 



(4) Terminals and Wiring 



—E (Terminal) 




Use the bolts (G) and nuts (H) 
to make two additional terminals 
as described under item VIII/A2, 
component (4) . Attach them to 
the base, just behind the upright, 
and then connect the clips and 
terminals with magnet wire (I) 
so that electrical connections 
exist between points A to A, 
B to B, C to C, D to D and E to 
E, thus insuring that once the 
additional terminals are con- 
nected to a circuit, the resul- 
tant current will flow through 
the two coils in the same 
direction. 



c . Notes 

(i) Changing the direction of the current through the moving coil will 
change the direction of the deflection, so long as the current through the 
multipurpose coils remains in the same direction. The resultant scale is 
thus a center zero scale, with the deflection indicating the direction of 
the current. So long as the current through the moving coil and the multi- 
purpose coils are independent of one another, this galvanometer cannot 
measure AC current. 

(ii) The galvanometer may be calibrated in the usual way by placing it 
in series with an ammeter (0 4 2 amps), a voltage supple (cells, battery, etc.) 
and a variable resistance. 

(iii) With a current of 0.25 amps flowing through the multipurpose coils, 
the galvanometer constructed had a range of to - 1.5 amps. When the 
current through the multipurpose coils was doubled to 0.50 amps the galvano- 
meter was much more sensitive, and the same deflections produced a range of 
to - 0.85 amps. 



-296- 



C3. Moving Coil Galvanometer with Shunts * 



(2) Electromagnet 



(1) Support 




(4) Scale and 
Pointer 



(3J Moving Coil 



a. Materials Reguired 
Components 
(1) Support 



q u Items Reguired 
1 Wood (A) 

1 Wood (B) 

1 Wood (C) 

1 Screw (D) 



Dimensions 

1 cm x 10 cm x 2 cm 

38 cm x 5 cm x 2 cm 

lOcmxlcmxlcm 

2.0 cm long 



* Adapted from Fr. George Schwarz, A Don Bosco Laboratory Manual, (Philippines: 
Unpublished Papers) . 



-297- 



(2) Electromagnet 



(3) Moving Coil 



1 Soft Iron Bar (E) 

Masking Tape (F) 

1 Bolt (G) 

1 Nut (H) 

1 Wing Nut (I) 

1 Magnet Wire (J) 

1 Bolt (K) 

2 Nuts (L) 

2 Bolts (M) 

4 Nuts (N) 

4 Thumbtacks (0) 

— Washers (P) 

1 Wooden Dowel (Q) 

2 Needles (R) 

1 Wooden Dowel (S) 





: 


Magnet Wire (T) 




2 


Magnet Wire (U) 




: 


Eye Screw (V) 




i 


Magnet Wire (W) 


(4) Pointer and 


: 


Soca Straw (X) 


Scale 







18 cm x 2.5 cm x 0.3 cm 

0.3 cm diameter, 
4 cm long 

0.3 cm internal 
diameter 

0.3 cm internal 
diameter 

#26 (0.05 cm diameter) , 
150 g 

0.4 cm diameter, 
3 cm long 

0.4 cm diameter 

0.3 cm diameter, 
3.5 cm long 

0.3 cm internal 
diameter 



0.6 cm internal 
diameter, 1.2 cm 
external diameter 

0.6 cm diameter, 
5.5 cm long 

0.1 cm diameter 

3.0 cm diameter, 
3.5 cm long 



Cardboard Sheet (Y) 



#26, 800 cm long 
#30, 16 cm long 

#26, 7 cm long 

5 cm length 

6 cm x 5 cm 



-298- 



b. Construction 



;i (Support 




Wire Support (C) 



Upright (B) 




Base (A) 



Use wood (A) for the base. Drill 
two screw holes in the base and 
attach a wooden upright (B) , as 
indicated, with the help of 
screws and glue. Make a slot 
1 cm wide, and ; cm deep, in the 
top of the upright to hold wood 
(C), the wire support. Drill a 
hole (0.2 cm diameter) at one end 
of the support, so that the 
latter may be attached to the up- 
right by means of a screw, and 
drill another hole (0.4 cm 
diameter) at the other end of the 
support to take a bolt. Attach 
the wire support to the upright 
with the help of the screw (D) 
and glue. 



-299- 



(2) Electromagnet 



Bolt Hole 



Masking 
Tape (F) 




Bar (E) 



Wire (J) 

Nut (H) \ 

/sxsrcoxccccxmax 






I 



*-*> — 30U( G) 



Bar (E) 



flUUUU.Q.UUU'X ' 



Wing Nut (I) 



Nut (L) 



/ 



Bol t (K) 
/ 



/ 

Support (C) Hole 



Side View 



Bend the soft iron bar (E) into 
a "U" shape with the parallel 
sides 4 cm apart. 

Wrap a layer of masking tape (F) 
around the bent bar, leaving 
the ends (3 cm lengths) clear. 
The tape will prevent the subse- 
guent magnet wire from being 
scraped and bared on any sharp 
edges. Bore a hole (0.3 cm 
diameter) in the middle of the 
base of the U-shaped bar. 
Insert the bolt (G) through the 
hole, and attach it firmly to 
the bar with the nut (H) . Wrap 
about 150 g of magnet wire (J) 
around the covered portion of the 
bar to make an electromagnet coil. 
Leave about 40 cm of free wire at 
either end of the coil. Cover 
the final layer of magnet wire 
with masking tape (F) to hold it 
firmly in position. 

Drill a hole (0.3 cm diameter) 
through the middle of the 
upright, and attach the newly 
made electromagnet to the up- 
right with the help of the 
protruding bolt and wing nut (I). 

Drill a small hole (0.2 cm 
diameter) through the end of 
the bolt (K) furthest from the 
head. Insert the bolt through 
the hole in the end of the wire 
support, and hold it in position 
with two nuts (L) as illustrated. 



wi re (J) 



Thumbtacks (0) 




Drill two holes (0.3 cm diameter) 
into the front of the base. 
Make two terminals from the 
nuts (N) and bolts (M) as 
described under item VIII/A2, 
component (4) . Set the terminals 
into the holes, making sure they 
are inset into the bottom of the 
base, thus leaving the bottom 
perfectly smooth. 

Fasten one of the wires from the 
electromagnet to a terminal on 
the base, and the other wire 
from the electromagnet to the 
bolt (K) on the wire support. 
Make sure the enamel has been 
removed from the wire ends 
prior to connection. Use 
thumbtacks (0) to hold the 
wires in position on the 
upright . 



Terminals 



(3) Moving Coil 




Needle (R) 
Dowel (Q) 

Washers (P) 



Needle (R) 



Slide the washers (P) onto the 
middle of the wooden dowel (Q) . 
Add the washers until they make 
a stack 3.5 cm long on the middle 
of the dowel. Use epoxy resin to 
fix the washers in position. 
Drill a hole (0.1 cm diameter, 
1 cm deep) into either end of 
the dowel. Cut two 2 cm lengths 
off the eye ends of the two 
needles (R) , and insert these 
into the newly drilled holes 
(needle eyes projecting) . Fix 
them firmly in position with the 
help of epoxy resin. 




Groove 



Dowel (S) 



Cut a groove (0.5 cm deep, 1 cm 
wide) around the wooden dowel (S) 
to hold the subsequent magnet 
wire coil in position. Drill a 
hole (1.2 cm diameter) along 
the axis of the spool, and insert 
the newly made stack of washers 
on the dowel (Q) . Use epoxy 
resin to hold this firmly in 
position within the dowel. 




Electrical 

Contact 



Rectangu lar 
Coil 



'Wire (T) 



Take the magnet wire (T) and 
wind it around the dowel (S) to 
make a rectangular coil contained 
within the groove which was cut 
for this purpose. Bare the ends 
of the wire, and wrap them 
around the stem of the top and 
bottom needles (R) respectively, 
insuring good electrical contact 
between magnet wire and needle. 



Wire (U) 




Wire (W) 



Eye Screw (V 



Bare one of the ends of the 
magnet wire (U) and wrap it 
around the eye of the needle in 
the top end of the dowel (S) . 
Suspend the dowel and coil by the 
wire, so that the dowel hangs 
between the pole ends of the 
electromagnet. With the dowel 
in this position, fasten the 
other end of the magnet wire to 
the hole in the bolt in the wire 
support (after cleaning the end 
of the magnet wire) . 

Take the second length of magnet 
wire (U) and attach one end 

(after cleaning) to the eye of th> 
needle in the bottom of the dowel 

(S) . Insert an eye screw (V) in 
the base, directly beneath the 
dowel, and connect the other 
end of the magnet wire (bared) 
to the screw. The slack should 
be taken out of this bottom 
magnet wire. 



Connect the eye screw to the 
unused terminal in the base by 
means of the remaining length 
of magnet wire (W) . 



(4) Pointer and Scale 



Straw (X) 



Slit 




A pointer for the galvanometer 
may be made from a soda straw (X) 
Make a small slit in the end, and 
fit it around the eye of the 
needle at the top of the dowel 

(S) . A little glue will hold 

it firmly in position. 

To make the scale, bend the 5 cm 
end of cardboard (Y) at 90° to 
make a 1 cm flap, and a flat 
surface 5 cm x 5 cm. Attach the 
cardboard to the upright 
(immediately beneath the pointer) 
with glue placed between the 
cardboard flap and the upright. 



Scale (Y) 



c. Notes 

(i) The galvanometer may be calibrated by placing it in series with an 
ammeter (0-1 amp), a voltage supply (dry cells, battery, etc.) and a variable 
resistance. The resultant scale will not be uniform. 

(ii) Changing the direction of the current through the moving coil changes 
the direction of the current through the electromagnet. As a result, the 
deflection of the pointer is always in the same direction, regardless of the 
direction of the current. The galvanometer thus measures AC and DC current 
egually well. (This would not be the case if a permanent magnet was used 
instead of the electromagnet.) 

(iii) Strictly speaking, the earth's magnetic field should be taken into 
consideration in using this galvanometer. For most purposes in the 



secondary school, this confounding factor may be ignored. Hence, in cali- 
brating the galvanometer 
it is useful to set the zero 
position of the coil at an 
angle to the line between 
the pole heads of the 
electromagnet, thus making 
full use of the scale. 




DC Amps 




(iv) The resistance of the galvanometer is 1. 



<S> 



; b 



to*. 



1.8 a 

0.2 
Shunt 



V. 




Shunt 



ohms. Hence, if a shunt of 
0.2 ohms is placed in 
parallel with the galvanometer, 
the scale of the latter will be 
multiplied by 10. The full 
scale deflection will thus 
correspond to 5 amp instead 

of 0.5 amp. Such a shunt may 
be made from a length of 
nichrome wire (approximately 
5 cm of #24 nichrome, 20% 
chrome and 80% nickel) 
connected between the terminals 
of the galvanometer. 



Top View 
(Cross-section) 



-305- 



(v) If a 250 ohm shunt is added in series to the galvanometer, it may be 

used as a voltmeter, the 
. 5 amp 



250 

rn/WWWVWWW 

Shunt 



^§> 



l.i 



Shunt 



WVWWVWWMr 



^AB 



125 volts 




full-scale deflection 
corresponding to 125 volts 
(DC) . One way of conveniently 
doing this is to add a 
third terminal [see VIII/A2, 
component (4)] to the front 
of the galvanometer base, simply 
placing the shunt (obtained from 
a radio shop) across two 
adjacent terminals. 



Top View 
(Cross-section) 



Voltmeter 

-Kv>— 



Variable 
Resistance 



-©- 



Galvanometer 
with Shunt 



The modified galvanometer 
may then be calibrated by 
placing it in parallel 
across a variable resistance, 
and comparing the potential 
at any moment with that 
indicated by a commercial 
voltmeter, also placed in 
parallel across the variable 
resistance. 



-306- 



BIBLIOGRAPHY 

A number of texts have proved to be extremely valuable references to 

the Inexpensive Science Teaching Equipment Project, and these are listed 

below. 

American Peace Corps, Science Teacher's Handbook, (Hyderabad: 

American Peace Corps, 1968) . 

This is a clear, well presented book 
which indicates how apparatus may be 
constructed for use in biology, chem- 
istry, and physics classes at an 
introductory level. 

The Association for Science Education, Science Master's Book, 



Part I of Series I to IV, Physics, (London: John Murray) . 

The material for this series has been 
selected from the School Science Review, 
which is published quarterly by the 
Association for Science Education. It 
contains details of the construction of 
many items of equipment, and describes 
related experiments for use in physics 
classes at the secondary level. 

Association for Science Education, The School Science Review, 

(London: John Murray). 

This is a quarterly journal which 
describes the construction of apparatus 
which may be used in the teaching of 
science at all levels. 

Bulman, A.D., Model Making for Young Physicist s, (London: 

John Murray, 1963) . 

This is a useful book which indicates 
how students might make some 30 items 
of physics equipment. 

Bulman, A.D., Experiments and Models for Young Physicist s, 

(London: John Murray, 1966) . 

This publication is on similar lines to the 
author's book indicated above, and contains 
descriptions of a further 18 items of 
equipment . 

Joseph, A., P.F. Brandwein, E. Morholt, H. Pollack and J.F. 

Castka, A Sourcebook for the Physical Sciences , (New York: Harcourt, 

Brace & World, Inc., 1961). 

This book offers not only a wide range 
of construction ideas, but also a whole 
series of suggestions for projects and 
experiments . 



-307- 



Melton, Reginald F., Elementary, Economic Experiments in 

Physics , (London : Centre for Educational Development Overseas, 1972) 

This is a four volume publication 
which provides not only details of 
apparatus construction and related 
experiments, but also provides much 
detailed information concerning 
laboratory and workshop facilities. 
It is intended for use at the sec- 
ondary level in developing countries. 

Merrick, P.D., Experiments with Plastic Syringes, (San Leandro, 

California: Educational Science Consultants, 1968). 

This book and the accompanying materials 
form a good basis for developing curriculum 
materials based on the disposable plastic 
syringe. 

Richardson, J.S. and G.P. Cahoon, Methods and Materials for 



Teaching General and Physical Science, (New York: McGraw-Hill Book 

Company, Inc., 1951) . 

This book contains a wide range of ideas 
for the making of physical science 
eguipment, and includes many related 
suggestions concerning techniques, skills 
and procedures . 

Stong, C.L., The Scientific American Book of Projects for the 

Amateur Scientist , (New York: Simon and Schuster, 1960) . 

The contents of this book are selected 
from Mr. Stong's clearing house of amateur 
activities, appearing monthly in Scientific 
American, and cover a wide range of ex- 
periments and related apparatus construction 
for all fields of science. 

United Nations Educational, Scientific and Cultural Organization, 

UNESCO Source Book for Science Teaching, (Paris: UNESCO, 1962) . 

This is one of the best resource books 
available for the construction of simple 
inexpensive science teaching equipment 
for use at all levels of teaching. 

In addition to the above texts the materials from a large number of 
projectinthe files of the International Clearinghouse on Science and 
Mathematics Curricular Developments at the University of Maryland have 
also been particularly valuable. Further details of these projects may 
be found in: 



The Seventh Report of the International Clearinghouse on 

Science and Mathematics Curricular Developments 1970, (Maryland, 

U.S.A.: University of Maryland, College Park, 1970). 

This is a source of information on 
curriculum pro jects throughout the 
world, and indicates materials 
available, project directors, pub- 
lishers, etc. The Eighth Report 
will be available in late 1972. 



-309- 



ALPHABETICAL INDEX 



Air Composition Device 

Alcohol Burner, Modified 

Alcohol Burner, Simple 

Ammeter, Hot Wire 

Ammeters (See Galvanometer) 

Anesthetizing Chamber 

Aperture/Slit Combination 

Aquarium, Breeding 

Aquarium, Jug or Carboy 

Aquarium, Plastic Bag 

Aquarium, Quickly Made Demonstration 

Aspirator 

Aspirator 

Baermann Funnel 
Balance, Compression Spring 
Balance, Current 
Balance, Equal Arm 
Balance, Extending Spring 
Balance, Micro- 
Balance, Pegboard 
Balance, Rubber Band 
Balance, Simple Beam 
Balance, Single Pan 
Balance, Soda Straw 
Balance, Spring 
Balance, Spring Lever 
Ball-and-stick Models 
Basket Sieve 
Bath, Sand 

Bath, Water or Steam 
Battery, Simple 
Beaker 

Beating Sheet 
Beehive Shelf 
Bell Jar 
Berlese Funnel 
Bi-metal Strip 



Page 
CHEM/2 66 
CHEM/40 
CHEM/38 
PHYS/255 

BIOL/261 
PHYS/113 
BIOL/147 
BIOL/146 
BIOL/148 
BIOL/145 
BIOL/103 
CHEM/117 

BIOL/114 

PHYS/12 

PHYS/261 

PHYS/24 

PHYS/9 

PHYS/22 

PHYS/17 

PHYS/5 

PHYS/8 

PHYS/32 

PHYS/20 

PHYS/36 

PHYS/2 

CHEM/193 

CHEM/127 

CHEM/18 8 

CHEM/189 

PHYS/185 

CHEM/109 

BIOL/101 

CHEM/173 

CHEM/111 

BIOL/117 

CHEM/59 



-310- 



Bird Trap, Potter 
Blowpipe for Charcoal Block 
Bottle, Specific Gravity 
Bottle, Wash 
Bottom Sampler 
Box Trap, Simple 
Bulb Holder with Bulb 
Burette 

Burette and Ring Stand with Attachments 
Burner, Candle 
Burner, Charcoal 
Burner, Fuel System for Gas- 
Burner, Gas 

Burner, Modified Alcohol- 
Burner, Simple Alcohol- 
Butterfly Net 

Cage, Ant Observation 

Cage, Cockroach 

Cage, Cylinder 

Cage, Glass 

Cage, Glass Jar 

Cage, Housefly 

Cage, Jar 

Cage, Wire 

Cage, Wooden Frame 

Candle Burner 

Carbon Dioxide Production Chamber 

Cart, Elementary 

Cart, Heavyweight 

Cart, Lightweight 

Cell, Chemical 

Cells, Dry Cell Holder with 

Centrifuge 

Centrifuge, Hand Drill 

Chamber, Transfer 

Charcoal Burner 

Charles' Law: Volume/Temperature Device 

Chemi cal Cell 

Chromatographic Device 

Chromatography Apparatus, Liquid-Column 



BIOL/126 

CHEM/191 

CHEM/69 

CHEM/114 

BIOL/82 

BIOL/119 

PHYS/191 

CHEM/61 

CHEM/90 

CHEM/35 

CHEM/36 

CHEM/43 

CHEM/4 9 

CHEM/40 

CHEM/38 

BIOL/94 

BIOL/173 

BIOL/163 

BIOL/167 

BIOL/176 

BIOL/159 

BIOL/165 

BIOL/169 

BIOL/185 

BIOL/180 

CHEM/35 

BIOL/269 

PHYS/61 

PHYS/75 

PHYS/66 

PHYS/177 

PHYS/180 

CHEM/153 

CHEM/149 

BIOL/226 

CHEM/36 

CHEM/252 

PHYS/177 

BIOL/255 

CHEM/237 



-311- 



Chromatography Device, Horizontal Paper 

Chromatography Device, Horizontal Paper 

Chromatography Device, Horizontal Paper 

Chromatography Equipment, Vertical Paper 

Chromatography Equipment, Vertical Paper Strip 

Circuit Board 

Clamp, Wooden Pinch 

Clamp, Wooden Screw 

Cleaner, Test Tube 

Clock, Classroom 

Clock, Water 

Collapsible Heating Stand 

Coil with Cores, Multipurpose 

Composition of Air Device 

Conductance Device 

Conductance Device, Constant Volume 

Condenser 

Cone Sieve 

Cover Slip, Glass Slide and 

Crystalline Packing Models 

Culture Flask 

Current Balance 

Decade Resistor 

Deflagrating "Spoon" 

Demonstration Thermometer 

Dessicator 

Diffraction Holes 

Diffusion Chamber 

Diffusion Device, Gas 

Diffusion Device, Liquid 

Dish, Petri 

Dissecting Needles 

Dissecting Pan 

Distillation Apparatus, Condenser 

Distillation Apparatus, Simple 

Double Bond Structures 

Dredge 

Dropper 

Dropper 

Dropper /Pipette 



CHEM/224 

CHEM/22 6 

CHEM/22 8 

CHEM/230 

CHEM/234 

PHYS/195 

CHEM/7 8 

CHEM/80 

CHEM/17 9 

PHYS/52 

PHYS/44 

CHEM/8 8 

PHYS/235 

CHEM/2 66 

CHEM/270 

CHEM/273 

CHEM/138 

CHEM/126 

BIOL/30 

CHEM/217 

BIOL/214 

PHYS/261 

PHYS/209 

CHEM/177 

CHEM/57 

CHEM/181 

PHYS/137 

BIOL/258 

CHEM/255 

CHEM/254 

CHEM/113 

BIOL/39 

BIOL/51 

CHEM/138 

CHEM/136 

CHEM/207 

BIOL/60 

BIOL/49 

CHEM/66 

CHEM/242 



Dry Cell Holder with Cells 
Dryer, Electric Lamp 
Drying Tower 
Dynamo/Motor 

Elasticity Device 
Electrolysis Apparatus 
Electroplating, Mirrors and 
Enzymatic Reaction Chamber 
Expansion Device, Gas 

Fermentation Tube, Balloon 
Fermentation Tube, Durham 
Fermentation Tube, Syringe 
Filter 

Filter Flask, Suction- 
Flame Test Wire 
Flask Generator (Gas) 
Flask, Light Bulb 
Flask, Suction-Filter 
Flasks, Volumetric 
Forceps 
Forceps 

Fuel System for Burners, Gas 
Funnel, Baermann 
Funnel, Berlese 
Funnel, Glass Bottle 
Funnel, Separatory 

Galvanometer, Elementary Moving Coil 

Galvanometer, Elementary Tangent 

Galvanometer, Moving Coil 

Galvanometer, Repulsion Type 

Galvanometer, Tangent 

Galvanometer with Multipurpose Coils, Moving Coil 

Galvanometer with Shunts, Moving Coil 

Galvanometer with Shunts, Tangent 

Gas Burner 

Gas Burner, Fuel System for 

Gas Collection Device, Plant 

Gas Collection Device, Seedling 

Gas Diffusion Device 



PHYS/180 
CHEM/185 
CHEM/183 
PHYS/217 

PHYS/102 
CHEM/145 
PHYS/116 
BIOL/263 
PHYS/103 

BIOL/247 

BIOL/248 

BIOL/249 

PHYS/128 

CHEM/12 9 

CHEM/17 6 

CHEM/165 

CHEM/107 

CHEM/12 9 

CHEM/68 

BIOL/48 

CHEM/72 

CHEM/43 

BIOL/114 

BIOL/117 

CHEM/110 

CHEM/132 

PHYS/266 

PHYS/246 

PHYS/285 

PHYS/249 

PHYS/272 

PHYS/292 

PHYS/296 

PHYS/276 

CHEM/4 9 

CHEM/43 

BIOL/265 

BIOL/267 

CHEM/255 



-313- 



Gas Expansion Device 
Gas Generator, Flask 
Gas Generator, Kipp's 

Gas Generator, Simple, and Collecting Apparatus 
Gas Production and Collection Device 
Gas Reaction Chamber 

Gas Solubility Device/Reaction Rate Chamber 
Gauze Wire 
Generator, Micro- 
Geometric Structures, Models 
Glass, Measuring 
Glass, Watch 
Glassware, Light Bulb 
Glassware Techniques and Accessories 
Grappling Ear 
Grappling Hook 
Growth Chamber, Plant 

Heating Shelf 

Heating Stand, Collapsible 

Holder, Multi-purpose Design 

Holder, Test Tube 

Hydraulic Press 

Hydrometer 

Incubator, Egg 

Incubator, Microorganism 

Indicator, Displacement Type Oxidation 

Indicator, Membrane Type Oxidation 

Indicator, Oxidation Rate 

Inoculating Needles 

Insect Collector, Night Flying 

Insect Spreading Board 

Interference Strips 

Jar, Bell 

Killing Jars 
Kinetic Theory Model 
Kipp ' s Generator 
Kymograph 

Lenses and Prisms, Optical 
Lens with Holder 



PHYS/103 

CHEM/165 

CHEM/167 

CHEM/163 

CHEM/245 

CHEM/2 68 

CHEM/250 

CHEM/82 

CHEM/2 4 9 

CHEM/215 

CHEM/64 

CHEM/112 

CHEM/109 

CHEM/1 

BIOL/87 

BIoL/85 

BIOL/155 

CHEM/83 
CHEM/8 8 
CHEM/73 
CHEM/7 6 
PHYS/96 
PHYS/108 

BIOL/200 

BIOL/219 

CHEM/2 60 

CHEM/2 5 8 

CHEM/262 

BIOL/218 

BIOL/105 

BIOL/99 

PHYS/138 

CHEM/111 

BIOL/96 
CHEM/220 
CHEM/167 
BIOL/234 

PHYS/121 
PHYS/130 



Light Bulb Glassware 

Light Bulb Glassware, Rack for 

Light Bulb Glassware, Stand for 

Light Source 

Liquid-Column Chromatographic Apparatus 

Liquid Diffusion Device 

Magnetic Field Apparatus 

Magnetic Field Apparatus with Multipurpose Coils 

Magnetizing Coil and Magnets 

Magnets 

Magnets, Magnetizing Coil at 

Magnifier, Illuminated Hand 

Magnifier, Water Filled 

Magnifying Glass, Water Bulb 

Manometer 

Masses, Box of 

Membrane-type Oxidation Indicator 

Measuring Glass 

Metal Sheet Shelf 

Microbalance 

Micro-generator 

Microscope, Adjustable 

Microscope, Glass Stage 

Microscope, Hand-Held 

Microscope, Match Box 

Microtome, Hand 

Mirrors and Electroplating 

Model, Kinetic Theory 

Models, Ball-and-stick 

Models, Crystalline Packing 

Model Units, Molecular 

Mortar and Pestle 

Motor/Dynamo 

Motor, Simple 

Moving Coil Galvanometer 

Moving Coil Galvanometer with Multipurpose Coils 

Moving Coil Galvanometer with Shunts 

Multipurpose Coil with Cores 

Multipurpose Design Holder 

Multipurpose Stand 



CHEM/107 
CHEM/100 
CHEM/102 
PHYS/111 
CHEM/237 
CHEM/2 54 

PHYS/238 

PHYS/241 

PHYS/231 

CHEM/125 

PHYS/231 

BIOL/7 

BIOL/2 

BIOL/3 

BIOL/251 

PHYS/30 

CHEM/258 

CHEM/64 

CHEM/74 

PHYS/22 

CHEM/2 4 9 

BIOL/24 

BIOL/14 

BIOL/19 

BIOL/21 

BIOL/35 

PHYS/116 

CHEM/220 

CHEM/193 

CHEM/217 

CHEM/198 

CHEM/120 

PHYS/217 

PHYS/212 

PHYS/285 

PHYS/292 

PHYS/296 

PHYS/235 

CHEM/73 

CHEM/98 



-J13- 



NeedHes, Inoculfeting 
Net, Butterfly 
Net, Dip 
Net, Lift 
Net, Plankton 

Optical Screen with Holder 
Optical Board and Accessories 
Oxidation Indicator, Displacement Type 
Oxidation Indicator, Membrane Type 
Oxidation Rate Indicator 

Pendulum, Simple 

Pestle, Mortar and 

Petri Dish 

Pipette 

Pipette/Dropper 

Pipette, Transfer 

Plankton Net 

Plant Growth Chamber 

Plant Press (Field Type) 

Plant Press (Laboratory Type) 

Press, Hydraulic 

Prisms and Lenses, Optical 

Pulse 

Pump 

Rack for Light Bulb Glassware 

Rack, Bamboo Text Tube 

Rack, Wooden Test Tube 

Rate Indicator, Oxidation 

Reaction Chamber, Gas 

Reaction Rate Chamber/Gas Solubility Device 

Rectifier, Silicon 

Rectifier (2 Plate) , Sodium Carbonate 

Refraction Model Apparatus 

Relaxing Jar 

Reptile Hook 

Resistor (Carbon) , Variable 

Resistor, Decade 

Resistor (Nichrome) , Variable 

Respirometer 



BIOL/218 

BIOL/94 

BIOL/54 

BIOL/71 

BIOL/65 

PHYS/124 
PHYS/119 
CHEM/2 60 
CHEM/258 
CHEM/2 62 

PHYS/50 

CHEM/120 

CHEM/113 

CHEM/67 

CHEM/242 

BIOL/224 

BIOL/65 

BIOL/155 

BIOL/140 

BIOL/142 

PHYS/96 

PHYS/121 

PHYS/49 

CHEM/243 

CHEM/100 

CHEM/103 

CHEM/105 

CHEM/2 62 

CHEM/268 

CHEM/250 

PHYS/168 

PHYS/162 

PHYS/126 

BIOL/98 

BIOL/132 

PHYS/202 

PHYS/209 

PHYS/204 

BIOL/270 



-316- 



Respirometer 

Ring and Burette Stand with Attachments 

Ripple Tank 

Ripple Tank Accessories 

Sand Bath 

Scalpel, Razor 

Scalpel, Strapping 

Scissors 

Screen, Hand 

Screen with Holder 

Screw Clamp, Wooden 

Seine, Two-Man 

Separatory Funnel 

Shelf, Beehive 

Shelf, Heating 

Shelf, Jar Cage 

Shelf, Metal Sheet 

Shunts, Tangent Galvanometer with 

Shunts, Moving Coil Galvanometer with 

Sieve, Basket 

Sieve, Cone 

Sieve, Soil Organism 

Single Bond Structures 

Slide and Cover Slip, Glass 

Slit, Adjustable Single 

Slit/Aperture Combination 

Slits, Fixed Single and Double 

Slits, Multiple 

Snare 

Soil Organism Sieve 

Source, Light 

Spatula 

Spatula, Test Tube Cleaner or 

Specific Gravity Bottle 

Specific Gravity Device 

"Spoon", Deflagrating 

Spreading Board, Insect 

Spring Balance 

Spring Balance, Compression 

Spring Balance, Extending 



BIOL/273 
CHEM/90 
PHYS/81 
PHYS/90 

CHEM/18 8 

BIOL/43 

BIOL/41 

BIOL/45 

BIOL/56 

PHYS/124 

CHEM/80 

BIOL/68 

CHEM/132 

CHEM/173 

CHEM/83 

BIOL/161 

CHEM/17 4 

PHYS/276 

PHYS/296 

CHEM/127 

CHEM/12 6 

BIOL/110 

CHEM/203 

BIOL/30 

PHYS/136 

PHYS/113 

PHYS/134 

PHYS/133 

BIOL/130 

BIOL/110 

PHYS/111 

CHEM/178 

CHEM717 9 

CHEM/69 

PHYS/107 

CHEM/177 

BIOL/99 

PHYS/36 

PHYS/12 

PHYS/9 



Stain Bottle 

Staining Vessel 

Stand, Collapsible Heating 

Stand for Light Bulb Glassware 

Stand, Multipurpose 

Stand with Attachments, Ring and Burette 

Steam or Water Bath 

Sterilizer 

Stick Models, Ball-and- 

Still, Water 

Stoichiometry Device 

Strapping Tripod 

Strip, Bi-metal 

Stroboscope 

Structures, Double Bond 

Structures, Geometric 

Structures, Single Bond 

Structures, Triple Bond 

Suction-Filter Flask 

Sun Dial 

Switch 

Tangent Galvanometer 

Tangent Galvanometer, Elementary 

Tangent Galvanometer with Shunts 

Tank, Ripple 

Techniques and Accessories, Glassware 

Temperature/Volume Device: Charles' Law 

Terrarium, Glass 

Terrarium, Simple 

Test Tube Cleaner or Spatula 

Test Tube Holder 

Test Tube Rack, Bamboo 

Test Tube Rack, Wooden 

Test Wire, Flame 

Thermometer, Demonstration 

Thermostat 

Timer, Ticker Tape 

Tower, Drying 

Transformer, Iron Wire Core 

(6 volt output, 120 volt mains) 



BIOL/33 

BIOL/31 

CHEM/8 8 

CHEM/102 

CHEM/98 

CHEM/90 

CHEM/18 9 

BIOL/215 

CHEM/193 

CHEM/141 

CHEM/2 63 

CHEM/8 6 

CHEM/5 9 

PHYS/93 

CHEM/207 

CHEM/215 

CHEM/203 

CHEM/213 

CHEM/12 9 

PHYS/41 

PHYS/193 

PHYS/272 

PHYS/246 

PHYS/276 

PHYS/81 

CHEM/1 

CHEM/252 

BIOL/153 

BIOL/151 

CHEM/179 

CHEM/76 

CHEM/103 

CHEM/105 

CHEM/17 6 

CHEM/57 

BIOL/207 

PHYS/56 

CHEM/183 

PHYS/140 



Transformer, Sheet Iron Core 

(12 volt output, 120 volt mains) 

Transformer, Variable Output 
(120 volt mains) 

Trap, Funnel 

Trap, Piling 

Trap, Potter Bird 

Trap, Simple Box 

Trap, Soil Insect 

Triple Bond Structures 

Tripod, Strapping 

Tripod, Tin Can 

Tripod, Wire 

Tweezers 

Units, Molecular Model 

Vacuum Apparatus 

Vasculum 

Vertical Paper Chromatography Equipment 

Vertical Strip Paper Chromatography Equipment 

Vivarium 

Voltmeters (See Galvanometers) 

Volume Determinator 

Volume/Temperature Device: Charles' Law 

Volumeter 

Volumetric Flasks 

Wash Bottle 

Watch Glass 

Water Glass 

Water or Steam Bath 

Water Still 

Wing Tip 

Wire Gauze 

Wire Tripod 

Wormery, Box 

Wormery, Jar 



PHYS/147 

PHYS/153 

BIOL/76 

BIOL/73 

BIOL/126 

BIOL/119 

BIOL/112 

CHEM/213 

CHEM/8 6 

CHEM/84 

CHEM/87 

CHEM/72 

CHEM/198 

PHYS/99 

BIOL/136 

CHEM/230 

CHEM/234 

BIOL/191 

PHYS/105 
CHEM/252 
BIOL/244 
CHEM/68 

CHEM/141 

CHEM/112 

BIOL/90 

CHEM/18 9 

CHEM/141 

CHEM/54 

CHEM182 

CHEM/8 7 

BIOL/171 

BIOL/168